6. ROM BIOS

    The design of the MSX ROM is of importance if machine code programs are to be developed efficiently and Operate reliably. Almost every program, including the BASIC Interpreter itself, will require a certain set of primitive functions to operate. These include screen and printer drivers, a keyboard decoder and other hardware related functions. By separating these routines from the BASIC Interpreter they can be made available to any application program. The section of ROM from 0000H to 268BH is largely devoted to such routines and is called the ROM BIOS (Basic Input Output System).

    This chapter gives a functional description of every recognizably separate routine in the ROM BIOS. Special attention is given to the "standard" routines. These are documented by Microsoft and guaranteed to remain consistent through possible hardware and software changes. The first few hundred bytes of the ROM consists of Z80 JP instructions which provide fixed position entry points to these routines. For maximum compatibility with future software an application program should restrict its dependence on the ROM to these locations only. The description of the ROM begins with this list of entry points to the standard routines. A brief comment is placed with each entry point, the full description is given with the routine itself.

Data Areas

    It is expected that most users will wish to disassemble the ROM to some extent (the full listing runs to nearly four hundred pages). In order to ease this process the data areas, which do not contain executable Z80 code, are shown below:

    0004H-0007H    185DH-1863H 4B3AH-4B4CH    73E4H-73E4H
    002BH-002FH    1B97H-1BAAH 4C2FH-4C3FH    752EH-7585H
    0508H-050DH    1BBFH-23BEH 555AH-5569H    7754H-7757H
    092FH-097FH    2439H-2459H 5D83H-5DB0H    7BA3H-7BCAH
    0DA5H-0EC4H    2CF1H-2E70H 6F76H-6F8EH    7ED8H-7F26H
    1033H-105AH    3030H-3039H 70FFH-710CH    7F41H-7FB6H
    1061H-10C1H    3710H-3719H 7182H-7195H    7FBEH-7FFFH
    1233H-1252H    392EH-3FE1H 71A2H-71B5H
    13A9H-1448H    43B5H-43C3H 71C7H-71DAH
    160BH-1612H    46E6H-46E7H 72A6H-72B9H

    Note that these data areas are for the UK ROM, there are slight differences in the Japanese ROM relating to the keyboard decoder and the video character set. Disparities between the ROMs are restricted to these regions with the bulk of the code being identical in both cases.

Terminology

    Reference is frequently made in this chapter to the standard routines and to Workspace Area variables. Whenever this is done the Microsoft-recommended name is used in upper case letters, for example "the FILVRM standard routine" and "SCRMOD is set". Subroutines which are not named are referred to by a parenthesized address, "the screen is cleared (0777H)" for example. When reference is made to the Z80 status flags assembly language conventions are used, for example "Flag C" would mean that the carry flag is set while "Flag NZ" means that the zero flag is reset. The terms "EI" and "DI" mean enabled interrupts and disabled interrupts respectively.

    Address ... 01B6H (from 000CH)
    Name ...... RDSLT (Read from Slot)
    Input ..... A=Slot ID, HL=Address
    Exit ...... A=Byte read
    Modifies .. AF, BC, DE, DI

    Standard routine to read a single byte from memory in any slot. The Slot Identifier is composed of a Primary Slot number a Secondary Slot number and a flag:

    7       6       5       4       3       2       1       0
+-------+-------+-------+-------+---------------+---------------+
| Flag  |   0   |   0   |   0   |Secondary Slot#| Primary Slot# |
+-------+-------+-------+-------+---------------+---------------+

Figure 34: Slot ID.

    The flag is normally 0 but must be 1 if a Secondary Slot number is included in the Slot ID. The memory address and Slot ID are first processed (027EH) to yield a set of bit masks to apply to the relevant slot register. If a Secondary Slot number is specified then the Secondary Slot Register is first modified to select the relevant page from that Secondary Slot (02A3H). The Primary Slot is then switched in to the Z80 address space, the byte read and the Primary Slot restored to its original setting via the RDPRIM routine in the Workspace Area. Finally, if a Secondary Slot number is included in the Slot ID, the original Secondary Slot Register setting is restored (01ECH).

    Note that, unless it is the slot containing the Workspace Area, any attempt to access page 3 (C000H to FFFFH) will cause the system to crash as RDPRIM will switch itself out. Note also that interrupts are left disabled by all the memory switching routines.

    Address ... 01D1H (from 0014H)
    Name ...... WRSLT (Write to Slot)
    Input ..... A=Slot ID, HL=Address, E=Byte to write
    Exit ...... None
    Modifies .. AF, BC, D, DI

    Standard routine to write a single byte to memory in any slot. Its operation is fundamentally the same as that of the RDSLT standard routine except that the Workspace Area routine WRPRIM is used rather than RDPRIM.

    BIOS Address .. 002BH
    Length ........ 5

    The bytes from 002BH to 002FH of the main ROM presents its version number and several other data, the MSX ROM Version Identification Bytes:

    002BH

      7   6   5   4   3   2   1   0
    +---+-----------+---------------+
    |VSF|Date Format| Character Set |
    +---+-----------+---------------+

    Character Set: 0000 (0) = Japan;
                   0001 (1) = International;
                   0010 (2) = U.S.S.R.

    Date Format: 000 (0) = Year/Month/Day (Japanese);
                 001 (1) = Month/Day/Year (U.S.A.);
                 010 (2) = Day/Month/Year (Latin countries).

    VSF (Vertical Synchronism   : 0 = 60 Hz (NTSC [Japan, U.S.A., U.S.S.R.],
    and interruption Frequency)              PAL-M [Brazil]);
                                  1 = 50 Hz (PAL-x [most European countries],
                                             SECAM [France]).

    002CH

      7   6   5   4   3   2   1   0
    +---+---+---+---+---------------+
    |Cur|SRC|SLS|SSM| Keyboard Type |
    +---+---+---+---+---------------+

    Keyboard Type: 0000 (0) = Japan;
                   0001 (1) = International;
                   0010 (2) = France;
                   0011 (3) = United Kingdom;
                   0100 (4) = Germany;
                   0101 (5) = USSR;
                   0110 (6) = Spain.

    SSM (Start-up : 0 = SCREEN 1 (Japan);
     Screen Mode)   1 = SCREEN 0 (International).

    SLS (String Length : 0 = ampersand ("&") (Japan);
          Specificator   1 = backslash ("\") (International).
          Character of
          PRINT USING)

    SRC (String  : 0 = "at" ("@") (Japan);
    Replacement    1 = ampersand ("&") (International).
    Character of
    PRINT USING)

    Currency : 0 = yen (Japan), pound (U.K.);
      Symbol   1 = dollar (U.S.A.).

    The PRINT USING characters' specification is necessary because the Japanese character set does not have the backslash. Instead, the japanese currency symbol "yen" is placed.

    002DH presents the MSX version:

00000000	(0)	= MSX
00000001	(1)	= MSX2
00000010	(2)	= MSX2+
00000011	(3)	= turbo R

    002EH

      7   6   5   4   3   2   1   0
    +---+---+---+---+---+---+---+---+
    | ? | ? | ? | ? | ? | ? | ? | ? |
    +---+---+---+---+---+---+---+---+


    002FH

      7   6   5   4   3   2   1   0
    +---+---+---+---+---+---+---+---+
    | ? | ? | ? | ? | ? | ? | ? | ? |
    +---+---+---+---+---+---+---+---+

    Address ... 0205H (from 0030H)
    Name ...... CALLF (Call Far routine)
    Input ..... None
    Exit ...... None
    Modifies .. AF', BC', DE', HL', IX, IY, DI

    Standard routine to call an address in any slot. The Slot ID and address are supplied as inline parameters rather than in registers to fit inside a hook (Chapter 6), for example:

RST 30H
DEFB Slot ID
DEFW Address
RET


    The Slot ID is first collected and placed in the high byte of register pair IY. The address is then placed in register pair IX and control drops into the CALSLT standard routine.

    Address ... 0217H (from 001CH)
    Name ...... CALSLT (Call Slot routine)
    Input ..... IY(High byte)=Slot ID, IX=Address
    Exit ...... None
    Modifies .. AF', BC', DE', HL', DI

    Standard routine to call an address in any slot. Its operation is fundamentally the same as that of the RDSLT standard routine except that the Workspace Area routine CLPRIM is used rather than RDPRIM. Note that CALBAS and CALLF are just specialized entry points to this standard routine which offer a reduction in the amount of code required.

    Address ... 025EH (from 0024H)
    Name ...... ENASLT (Enable Slot)
    Input ..... A=Slot ID, HL=Address
    Exit ...... None
    Modifies .. AF, BC, DE, DI

    Standard routine to switch in a page permanently from any slot. Unlike the RDSLT, WRSLT and CALSLT standard routines the Primary Slot switching is performed directly and not by a Workspace Area routine. Consequently addresses in page 0 (0000H to 3FFFH) will cause an immediate system crash.

Address

027EH (MSX only)

    This routine is used by the memory switching standard routines to turn an address, in register pair HL, and a Slot ID, in register A, into a set of bit masks. As an example a Slot ID of FxxxSSPP and an address in Page 1 (4000H to 7FFFH) would return the following:

        Register B=00 00 PP 00 (OR mask)
        Register C=11 11 00 11 (AND mask)
        Register D=PP PP PP PP (Replicated)
        Register E=00 00 11 00 (Page mask)

    Registers B and C are derived from the Primary Slot number and the page mask. They are later used to mix the new Primary Slot number into the existing contents of the Primary Slot Register. Register D contains the Primary Slot number replicated four times and register E the page mask. This is produced by examining the two most significant bits of the address, to determine the page number, and then shifting the mask along to the relevant position. These registers are later used during Secondary Slot switching.

    As the routine terminates bit 7 of the Slot ID is tested, to determine whether a Secondary Slot has been specified, and Flag M returned if this is so.

Address

02A3H (MSX only)

    This routine is used by the memory switching standard routines to modify a Secondary Slot Register. The Slot ID is supplied in register A while registers D and E contain the bit masks shown in the previous routine.

    Bits 6 and 7 of register D are first copied into the Primary Slot register. This switches in page 3 from the Primary Slot specified by the Slot ID and makes the required Secondary Slot Register available. This is then read from memory location FFFFH and the page mask, inverted, used to clear the required two bits. The Secondary Slot number is shifted to the relevant position and mixed in. Finally the new setting is placed in the Secondary Slot Register and the Primary Slot Register restored to its original setting.

    Address ... 02D7H (from 0000H)
    Name ...... CHKRAM (Check RAM)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, HL, SP

    Standard routine to perform memory initialization at power- up. It non-destructively tests for RAM in pages 2 and 3 in all sixteen possible slots then sets the Primary and Secondary Slot registers to switch in the largest area found. The entire Workspace Area (F380H to FFC9H) is zeroed and EXPTBL and SLTTBL filled in to map any expansion interfaces in existence Interrupt Mode 1 is set and control transfers to the remainder of the power-up initialization routine (7C76H).

    Address ... 03FBH (from 00BAH)
    Name ...... ISCNTC (Is Control-stop)
    Input ..... None
    Exit ...... None
    Modifies .. AF, EI

    Standard routine to check whether the CTRL-STOP or STOP keys have been pressed. It is used by the BASIC Interpreter at the end of each statement to check for program termination. BASROM is first examined to see if it contains a non-zero value, if so the routine terminates immediately. This is to prevent users breaking into any extension ROM containing a BASIC program.

    INTFLG is then checked to determine whether the interrupt handler has placed the CTRL-STOP or STOP key codes (03H or 04H) there. If STOP has been detected then the cursor is turned on (09DAH) and INTFLG continually checked until one of the two key codes reappears. The cursor is then turned off (0A27H) and, if the key is STOP, the routine terminates.

    If CTRL-STOP has been detected then the keyboard buffer is first cleared via the KILBUF standard routine and TRPTBL is checked to see whether an "ON STOP GOSUB" statement is active. If so the relevant entry in TRPTBL is updated (0EF1H) and the routine terminates as the event will be handled by the Interpreter Runloop. Otherwise the ENASLT standard routine is used to switch in page 1 from the MSX ROM, in case an extension ROM is using the routine, and control transfers to the "STOP" statement handler (63E6H).

    Address ... 0468H (from 0156H)
    Name ...... KILBUF (Kill keyboard Buffer)
    Input ..... None
    Exit ...... None
    Modifies .. HL

    Standard Routine to clear the forty character type-ahead keyboard buffer KEYBUF. There are two pointers into this buffer, PUTPNT where the interrupt handler places characters, and GETPNT where application programs fetch them from. As the number of characters in the buffer is indicated by the difference between these two pointers KEYBUF is emptied simply by making them both equal.

    BIOS Address .. 0159H
    Name .......... CALBAS (Call BASIC interpreter routine)
    Entry ......... IX=Address
    Exit .......... None
    Modifies ...... AF', BC', DE', HL', IY, DI

    Standard routine to call an address in the BASIC Interpreter from any slot. Usually this will be from a machine code program running in an extension ROM in page 1 (4000H to 7FFFH). The high byte of register pair IY is loaded with the MSX ROM Slot ID (00H) and control transfers to the CALSLT standard routine.

    Deprecated entry point 01FFH on some european MSX.

    Address ... 046FH (from 00B7H)
    Name ...... BREAKX (Break eXecution)
    Input ..... None
    Exit ...... Flag C if CTRL-STOP key pressed
    Modifies .. AF

    Standard routine which directly tests rows 6 and 7 of the keyboard to determine whether the CTRL and STOP keys are both pressed. If they are then KEYBUF is cleared and row 7 of OLDKEY modified to prevent the interrupt handler picking the keys up as well. This routine may often be more suitable for use by an application program, in preference to ISCNTC, as it will work when interrupts are disabled, during cassette I/O for example, and does not exit to the Interpreter.

    Address ... 049DH (from 003BH)
    Name ...... INITIO (Initialize PSG I/O ports)
    Input ..... None
    Exit ...... None
    Modifies .. AF, E, EI

    Standard routine to initialize the PSG and the Centronics Status Port. PSG Register 7 is first set to 80H making PSG Port B=Output and PSG Port A=Input. PSG Register 15 is set to CFH to initialize the Joystick connector control hardware. PSG Register 14 is then read and the Keyboard Mode bit placed in KANAMD, this has no relevance for UK machines.

    Finally a value of FFH is output to the Centronics Status Port (I/O port 90H) to set the STROBE signal high. Control then drops into the GICINI standard routine to complete initialization.

    Address ... 04BDH (from 0090H)
    Name ...... GICINI (General Instruments PSG Control Initialization)
    Input ..... None
    Exit ...... None
    Modifies .. EI

    Standard routine to initialize the PSG and the Workspace Area variables associated with the "PLAY" statement. QUETAB, VCBA, VCBB and VCBC are first initialized with the values shown in Chapter 6. PSG Registers 8, 9 and 10 are then set to zero amplitude and PSG Register 7 to B8H. This enables the Tone Generator and disables the Noise Generator on each channel.

Address

@ (MSX only)

    This six byte table contains the "PLAY" statement parameters initially placed in VCBA, VCBB and VCBC by the GICINI standard routine: Octave=4, Length=4, Tempo=120, Volume=88H, Envelope=00FFH.

    Address ... 050EH (from 006CH)
    Name ...... INITXT (Initialize Text mode)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to initialize the VDP to 40x24 Text Mode. The screen is temporarily disabled via the DISSCR standard routine and SCRMOD and OLDSCR set to 00H. The parameters required by the CHPUT standard routine are set up by copying LINL40 to LINLEN, TXTNAM to NAMBAS and TXTCGP to CGPBAS. The VDP colours are then set by the CHGCLR standard routine and the screen is cleared (077EH). The current character set is copied into the VRAM Character Pattern Table (071EH). Finally the VDP mode and base addresses are set via the SETTXT standard routine and the screen is enabled.

    Address ... 0538H (from 006FH)
    Name ...... INIT32 (Initialize Text 32 mode)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to initialize the VDP to 32x24 Text Mode. The screen is temporarily disabled via the DISSCR standard routine and SCRMOD and OLDSCR set to 01H. The parameters required by the CHPUT standard routine are set up by copying LINL32 to LINLEN, T32NAM to NAMBAS, T32CGP to CGPBAS, T32PAT to PATBAS and T32ATR to ATRBAS. The VDP colours are then set via the CHGCLR standard routine and the screen is cleared (077EH). The current character set is copied into the VRAM Character Pattern Table (071EH) and all sprites cleared (06BBH). Finally the VDP mode and base addresses are set via the SETT32 standard routine and the screen is enabled.

    Address ... 0570H (from 0044H)
    Name ...... ENASCR (Enable Screen)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, EI

    Standard routine to enable the screen. This simply involves setting bit 6 of VDP Mode Register 1.

    Address ... 0577H (from 0041H)
    Name ...... DISSCR (Disable Screen)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, EI

    Standard routine to disable the screen. This simply involves resetting bit 6 of VDP Mode Register 1.

    Address ... 057FH (from 0047H)
    Name ...... WRTVDP (Write to VDP Register)
    Input ..... B=Data byte, C=VDP Mode Register number
    Exit ...... None
    Modifies .. AF, B, EI

    Standard routine to write a data byte to any VDP Mode Register. The register selection byte is first written to the VDP Command Port, followed by the data byte. This is then copied to the relevant register image, RG0SAV to RG7SAV, in the Workspace Area (on MSX2, MSX2+ and turbo R, variables from RG8SAV till RG23SA and from RG25SA till RG27SA are also set, accordingly).

    Address ... 0594H (from 0078H)
    Name ...... SETTXT (Set Text mode)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to partially set the VDP to 40x24 Text Mode. The mode bits M1, M2 and M3 are first set in VDP Mode Registers 0 and 1. The five VRAM table base addresses, beginning with TXTNAM, are then copied from the Workspace Area into VDP Mode Registers 2, 3, 4, 5 and 6 (0677H).

    Address ... 05B4H (from 007BH)
    Name ...... SETT32 (Set Text 32 mode)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to partially set the VDP to 32x24 Text Mode. The mode bits M1, M2 and M3 are first set in VDP Mode Registers 0 and 1. The five VRAM table base addresses, beginning with T32NAM, are then copied from the Workspace Area into VDP Mode Registers 2, 3, 4, 5 and 6 (0677H).

    Address ... 05D2H (from 0072H)
    Name ...... INIGRP (Initialize Graphic mode)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to initialize the VDP to Graphics Mode. The screen is temporarily disabled via the DISSCR standard routine and SCRMOD set to 02H. The parameters required by the GRPPRT standard routine are set up by copying GRPPAT to PATBAS and GRPATR to ATRBAS. The character code driver pattern is then copied into the VDP Name Table, the screen cleared (07A1H) and all sprites cleared (06BBH). Finally the VDP mode and base addresses are set via the SETGRP standard routine and the screen is enabled.

    Address ... 0602H (from 007EH)
    Name ...... SETGRP (Set Graphic mode)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to partially set the VDP to Graphics Mode. The mode bits M1, M2 and M3 are first set in VDP Mode Registers 0 and 1. The five VRAM table base addresses, beginning with GRPNAM, are then copied from the Workspace Area into VDP Mode Registers 2, 3, 4, 5 and 6 (0677H).

    Address ... 061FH (from 0075H)
    Name ...... INIMLT (Initialize Multicolour mode)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to initialize the VDP to Multicolour Mode. The screen is temporarily disabled via the DISSCR standard routine and SCRMOD set to 03H. The parameters required by the GRPPRT standard routine are set up by copying MLTPAT to PATBAS and MLTATR to ATRBAS. The character code driver pattern is then copied into the VDP Name Table, the screen cleared (07B9H) and all sprites cleared (06BBH). Finally the VDP mode and base addresses are set via the SETMLT standard routine and the screen is enabled.

    Address ... 0659H (from 0081H)
    Name ...... SETMLT (Set Multicolour mode)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to partially set the VDP to Multicolour Mode. The mode bits M1, M2 and M3 are first set in VDP Mode Registers 0 and 1. The five VRAM table base addresses, beginning with MLTNAM, are then copied from the Workspace Area to VDP Mode Registers 2, 3, 4, 5 and 6.

Address

@ (MSX only)

    This routine is used by the SETTXT, SETT32, SETGRP and SETMLT standard routines to copy a block of five table base addresses from the Workspace Area into VDP Mode Registers 2, 3, 4, 5 and 6. On entry register pair HL points to the relevant group of addresses. Each base address is collected in turn, shifted the required number of places and then written to the relevant Mode Register via the WRTVDP standard routine.

    Address ... 06A8H (from 0069H)
    Name ...... CLRSPR (Clear all Sprites)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to clear all sprites. The entire 2 KB Sprite Pattern Table is first filled with zeros via the FILVRM standard routine. The vertical coordinate of each of the thirty-two sprite attribute blocks is then set to -47 (D1H) to place the sprite above the top of the screen, the horizontal coordinate is left unchanged.

    The pattern numbers in the Sprite Attribute Table are initialized with the series 0, 1, 2, 3, 4,... 31 for 8x8 sprites or the series 0, 4, 8, 12, 16,... 124 for 16x16 sprites. The series to be generated is determined by the Size bit in VDP Mode Register 1. Finally the colour byte of each sprite attribute block is filled in with the colour code contained in FORCLR, this is initially white.

    Note that the Size and Mag bits in VDP Mode Register 1 are not affected by this routine. Note also that the INIT32, INIGRP and INIMLT standard routines use this routine with an entry point at 06BBH, leaving the Sprite Pattern Table undisturbed.

    Address ... 06E4H (from 0084H)
    Name ...... CALPAT (Calculate sprite Pattern address)
    Input ..... A=Sprite pattern number
    Exit ...... HL=Sprite pattern address
    Modifies .. AF, DE, HL

    Standard routine to calculate the address of a sprite pattern. The pattern number is first multiplied by eight then, if 16x16 sprites are selected, multiplied by a further factor of four. This is then added to the Sprite Pattern Table base address, taken from PATBAS, to produce the final address.

    This numbering system is in line with the BASIC Interpreter's usage of pattern numbers rather than the VDP's when 16x16 sprites are selected. As an example while the Interpreter calls the second pattern number one, it is actually VDP pattern number four. This usage means that the maximum pattern number this routine should allow, when 16x16 sprites are selected, is sixty-three. There is no actual check on this limit so large pattern numbers will produce addresses greater than 3FFFH. Such addresses, when passed to the other VDP routines, will wrap around past zero and corrupt the Character Pattern Table in VRAM.

    Address ... 06F9H (from 0087H)
    Name ...... CALATR (Calculate sprite Attribute address)
    Input ..... A=Sprite number
    Exit ...... HL=Sprite attribute address
    Modifies .. AF, DE, HL

    Standard routine to calculate the address of a sprite attribute block. The sprite number, from zero to thirty-one, is multiplied by four and added to the Sprite Attribute Table base address taken from ATRBAS.

    Address ... 0704H (from 008AH)
    Name ...... GSPSIZ (Get Sprite Pattern Size)
    Input ..... None
    Exit ...... A=Bytes in sprite pattern (8 or 32)
    Modifies .. AF

    Standard routine to return the number of bytes occupied by each sprite pattern in the Sprite Pattern Table. The result is determined simply by examining the Size bit in VDP Mode Register 1.

    Address ... 070FH (from 0059H)
    Name ...... LDIRMV (Load, Increment and Repeat to Memory from VRAM)
    Input ..... BC=Length, DE=RAM address, HL=VRAM address
    Exit ...... None
    Modifies .. AF, BC, DE, EI

    Standard routine to copy a block into main memory from the VDP VRAM. The VRAM starting address is set via the SETRD standard routine and then sequential bytes read from the VDP Data Port and placed in main memory.

Address

@ (MSX only)

    This routine is used to copy a 2 KB character set into the VDP Character Pattern Table in any mode. The base address of the Character Pattern Table in VRAM is taken from CGPBAS. The starting address of the character set is taken from CGPNT. The RDSLT standard routine is used to read the character data so this may be situated in an extension ROM.

    At power-up CGPNT is initialized with the address contained at ROM location 0004H, which is 1BBFH. CGPNT is easily altered to produce some interesting results, POKE &HF920,&HC7:SCREEN 0 provides a thoroughly confusing example.

    Address ... 0744H (from 005CH)
    Name ...... LDIRVM (Load, Increment and Repeat to VRAM from Memory)
    Input ..... BC=Length, DE=VRAM address, HL=RAM address
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to copy a block to VRAM from main memory. The VRAM starting address is set via the SETWRT standard routine and then sequential bytes taken from main memory and written to the VDP Data Port.

Address

@ (MSX only)

    This routine will clear the screen in any VDP mode. In 40x24 Text Mode and 32x24 Text Mode the Name Table, whose base address is taken from NAMBAS, is first filled with ASCII spaces. The cursor is then set to the home position (0A7FH) and LINTTB, the line termination table, re-initialized. Finally the function key display is restored, if it is enabled, via the FNKSB standard routine.

    In Graphics Mode the border colour is first set via VDP Mode Register 7 (0832H). The Colour Table is then filled with the background colour code, taken from BAKCLR, for both 0 and 1 pixels. Finally the Character Pattern Table is filled with zeroes.

    In Multicolour Mode the border colour is first set via VDP Mode Register 7 (0832H). The Character Pattern Table is then filled with the background colour taken from BAKCLR.

    Address ... 07CDH (from 004DH)
    Name ...... WRTVRM (Write to VRAM)
    Input ..... A=Data byte, HL=VRAM address
    Exit ...... None
    Modifies .. EI

    Standard routine to write a single byte to the VDP VRAM. The VRAM address is first set up via the SETWRT standard routine and then the data byte written to the VDP Data Port. Note that the two seemingly spurious EX(SP),HL instructions in this routine, and several others, are required to meet the VDP's timing constraints.

    Address ... 07D7H (from 004AH)
    Name ...... RDVRM (Read from VRAM)
    Input ..... HL=VRAM address
    Exit ...... A=Byte read
    Modifies .. AF, EI

    Standard routine to read a single byte from the VDP VRAM. The VRAM address is first set up via the SETRD standard routine and then the byte read from the VDP Data Port.

    Address ... 07DFH (from 0053H)
    Name ...... SETWRT (Set VDP for Writing)
    Input ..... HL=VRAM address
    Exit ...... None
    Modifies .. AF, EI

    Standard routine to set up the VDP for subsequent writes to VRAM via the Data Port. The address contained in register pair HL is written to the VDP Command Port LSB first, MSB second as shown in Figure 7. Addresses greater than 3FFFH will wrap around past zero as the two most significant bits of the address are ignored.

    Address ... 07ECH (from 0050H)
    Name ...... SETRD (Set VDP for Reading)
    Input ..... HL=VRAM address
    Exit ...... None
    Modifies .. AF, EI

    Standard routine to set up the VDP for subsequent reads from VRAM via the Data Port. The address contained in register pair HL is written to the VDP Command Port LSB first, MSB second as shown in Figure 7. Addresses greater than 3FFFH will wrap around past zero as the two most significant bits of the address are ignored.

    Address ... 07F7H (from 0062H)
    Name ...... CHGCLR (Change Colour)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, HL, EI

    Standard routine to set the VDP colours. SCRMOD is first examined to determine the appropriate course of action. In 40x24 Text Mode the contents of BAKCLR and FORCLR are written to VDP Mode Register 7 to set the colour of the 0 and 1 pixels, these are initially blue and white. Note that in this mode there is no way of specifying the border colour, this will be the same as the 0 pixel colour. In 32x24 Text Mode, Graphics Mode or Multicolour Mode the contents of BDRCLR are written to VDP Mode Register 7 to set the colour of the border, this is initially blue. Also in 32x24 Text Mode the contents of BAKCLR and FORCLR are copied to the whole of the Colour Table to determine the 0 and 1 pixel colours.

    Address ... 0815H (from 0056H)
    Name ...... FILVRM (Fill VRAM)
    Input ..... A=Data byte, BC=Length, HL=VRAM address
    Exit ...... None
    Modifies .. AF, BC, EI

    Standard routine to fill a block of the VDP VRAM with a single data byte. The VRAM starting address, contained in register pair HL, is first set up via the SETWRT standard routine. The data byte is then repeatedly written to the VDP Data Port to fill successive VRAM locations.

    Address ... 083BH (from 00D2H)
    Name ...... TOTEXT (To Text mode)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to return the VDP to either 40x24 Text Mode or 32x24 Text Mode if it is currently in Graphics Mode or Multicolour Mode. It is used by the BASIC Interpreter Mainloop and by the "INPUT" statement handler. Whenever the INITXT or INIT32 standard routines are used the mode byte, 00H or 01H, is copied into OLDSCR. If the mode is subsequently changed to Graphics Mode or Multicolour Mode, and then has to be returned to one of the two text modes for keyboard input, this routine ensures that it returns to the same one.

    SCRMOD is first examined and, if the screen is already in either text mode, the routine simply terminates with no action. Otherwise the previous text mode is taken from OLDSCR and passed to the CHGMOD standard routine.

    Address ... 0848H (from 00C3H)
    Name ...... CLS (Clear Screen)
    Input ..... Flag Z
    Exit ...... None
    Modifies .. AF, BC, DE, EI

    Standard routine to clear the screen in any mode, it does nothing but call the routine at 0777H. This is actually the "CLS" statement handler and, because this indicates that there is illegal text after the statement, it will simply return if entered with Flag NZ.

    Address ... 084FH (from 005FH)
    Name ...... CHGMOD (Change screen Mode)
    Input ..... A=Screen mode required (0, 1, 2, 3)
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to set a new screen mode. Register A, containing the required screen mode, is tested and control transferred to INITXT, INIT32, INIGRP or INIMLT.

    Address ... 085DH (from 00A5H)
    Name ...... LPTOUT (Line Printer Output)
    Input ..... A=Character to print
    Exit ...... Flag C if CTRL-STOP termination
    Modifies .. AF

    Standard routine to output a character to the line printer via the Centronics Port. The printer status is continually tested, via the LPTSTT standard routine, until the printer becomes free. The character is then written to the Centronics Data Port (I/O port 91H) and the STROBE signal of the Centronics Status Port (I/O port 90H) briefly pulsed low. Note that the BREAKX standard routine is used to test for the CTRL- -STOP key if the printer is busy. If CTRL-STOP is detected a CR code is written to the Centronics Data Port, to flush the printer's line buffer, and the routine terminates with Flag C.

    Address ... 0884H (from 00A8H)
    Name ...... LPTSTT (Line Printer Status Test)
    Input ..... None
    Exit ...... A=0 and Flag Z if printer busy
    Modifies .. AF

    Standard routine to test the Centronics Status Port BUSY signal. This just involves reading I/O port 90H and examining the state of bit 1: 0=Ready, 1=Busy.

    Address ... 088EH (from 00C6H)
    Name ...... POSIT (Position cursor)
    Input ..... H=Column, L=Row
    Exit ...... None
    Modifies .. AF, EI

    Standard routine to set the cursor coordinates. The row and column coordinates are sent to the OUTDO standard routine as the parameters in an ESC,"Y",Row+1FH, Column+1FH sequence. Note that the BIOS home position has coordinates of 1,1 rather than the 0,0 used by the BASIC Interpreter.

    Address ... 089DH (from 00ABH)
    Name ...... CNVCHR (Convert Character)
    Input ..... A=Character
    Exit ...... Flag Z, NC=Header
               Flag NZ, C=Graphic
               Flag Z, C=Normal
    Modifies .. AF

    Standard routine to test for, and convert if necessary, characters with graphic headers. Characters less than 20H are normally interpreted by the output device drivers as control characters. A character code in this range can be treated as a displayable character by preceding it with a graphic header control code (01H) and adding 40H to its value. For example to directly display character code 0DH, rather than have it interpreted as a carriage return, it is necessary to output the two bytes 01H,4DH. This routine is used by the output device drivers, such as the CHPUT standard routine, to check for such sequences.

    If the character is a graphic header GRPHED is set to 01H and the routine terminates, otherwise GRPHED is zeroed. If the character is outside the range 40H to 5FH it is left unchanged. If it is inside this range, and GRPHED contains 01H indicating a previous graphic header, it is converted by subtracting 40H.

    Address ... 08BCH (from 00A2H)
    Name ...... CHPUT (Character Put)
    Input ..... A=Character
    Exit ...... None
    Modifies .. EI

    Standard routine to output a character to the screen in 40x24 Text Mode or 32x24 Text Mode. SCRMOD is first checked and, if the VDP is in either Graphics Mode or Multicolour Mode, the routine terminates with no action. Otherwise the cursor is removed (0A2EH), the character decoded (08DFH) and then the cursor replaced (09E1H). Finally the cursor column position is placed in TTYPOS, for use by the "PRINT" statement, and the routine terminates.

Address

@ (MSX only)

    This routine is used by the CHPUT standard routine to decode a character and take the appropriate action. The CNVCHR standard routine is first used to check for a graphic character, if the character is a header code (01H) then the routine terminates with no action. If the character is a converted graphic one then the control code decoding section is skipped. Otherwise ESCCNT is checked to see if a previous ESC character (1BH) has been received, if so control transfers to the ESC sequence processor (098FH). Otherwise the character is checked to see if it is smaller than 20H, if so control transfers to the control code processor (0914H). The character is then checked to see if it is DEL (7FH), if so control transfers to the delete routine (0AE3H).

    Assuming the character is displayable the cursor coordinates are taken from CSRY and CSRX and placed in register pair HL, H=Column, L=Row. These are then converted to a physical address in the VDP Name Table and the character placed there (0BE6H). The cursor column position is then incremented (0A44H) and, assuming the rightmost column has not been exceeded, the routine terminates. Otherwise the row's entry in LINTTB, the line termination table, is zeroed to indicate an extended logical line, the column number is set to 01H and a LF is performed.

Address

@ (MSX only)

    This routine performs the LF operation for the CHPUT standard routine control code processor. The cursor row is incremented (0A61H) and, assuming the lowest row has not been exceeded, the routine terminates. Otherwise the screen is scrolled upwards and the lowest row erased (0A88H).

Address

@ (MSX only)

    This is the control code processor for the CHPUT standard routine. The table at 092FH is searched for a match with the code and control transferred to the associated address.

Address

@ (MSX only)

    This table contains the control codes, each with an associated address, recognized by the CHPUT standard routine:

        CODE TO     FUNCTION
        -------------------------------------------------
        07H  1113H  BELL, go beep
        08H  0A4CH  BS, cursor left
        09H  0A71H  TAB, cursor to next tab position
        0AH  0908H  LF, cursor down a row
        0BH  0A7FH  HOME, cursor to home
        0CH  077EH  FORMFEED, clear screen and home
        0DH  0A81H  CR, cursor to leftmost column
        1BH  0989H  ESC, enter escape sequence
        1CH  0A5BH  RIGHT, cursor right
        1DH  0A4CH  LEFT, cursor left
        1EH  0A57H  UP, cursor up
        1FH  0A61H  DOWN, cursor down.

Address

@ (MSX only)

    This table contains the ESC control codes, each with an associated address, recognized by the CHPUT standard routine:

        CODE TO     FUNCTION
        -------------------------------------------------
        6AH  077EH  ESC,"j", clear screen and home
        45H  077EH  ESC,"E", clear screen and home
        4BH  0AEEH  ESC,"K", clear to end of line
        4AH  0B05H  ESC,"J", clear to end of screen
        6CH  0AECH  ESC,"l", clear line
        4CH  0AB4H  ESC,"L", insert line
        4DH  0A85H  ESC,"M", delete line
        59H  0986H  ESC,"Y", set cursor coordinates
        41H  0A57H  ESC,"A", cursor up
        42H  0A61H  ESC,"B", cursor down
        43H  0A44H  ESC,"C", cursor right
        44H  0A55H  ESC,"D", cursor left
        48H  0A7FH  ESC,"H", cursor home
        78H  0980H  ESC,"x", change cursor
        79H  0983H  ESC,"y", change cursor

Address

@ (MSX only)

    This routine performs the ESC,"x" operation for the CHPUT standard routine control code processor. ESCCNT is set to 01H to indicate that the next character received is a parameter.

Address

@ (MSX only)

    This routine performs the ESC,"y" operation for the CHPUT standard routine control code decoder. ESCCNT is set to 02H to indicate that the next character received is a parameter.

Address

@ (MSX only)

    This routine performs the ESC",Y" operation for the CHPUT standard routine control code processor. ESCCNT is set to 04H to indicate that the next character received is a parameter.

Address

@ (MSX only)

    This routine performs the ESC operation for the CHPUT standard routine control code processor. ESCCNT is set to FFH to indicate that the next character received is the second control character.

Address

@ (MSX only)

    This is the CHPUT standard routine ESC sequence processor. If ESCCNT contains FFH then the character is the second control character and control transfers to the control code processor (0919H) to search the ESC code table at 0953H.

    If ESCCNT contains 01H then the character is the single parameter of the ESC,"x" sequence. If the parameter is "4" (34H) then CSTYLE is set to 00H resulting in a block cursor. If the parameter is "5" (35H) then CSRSW is set to 00H making the cursor normally disabled.

    If ESCCNT contains 02H then the character is the single parameter in the ESC,"y" sequence. If the parameter is "4" (34H) then CSTYLE is set to 01H resulting in an underline cursor. If the parameter is "5" (35H) then CSRSW is set to 01H making the cursor normally enabled.

    If ESCCNT contains 04H then the character is the first parameter of the ESC,"Y" sequence and is the row coordinate. The parameter has 1FH subtracted and is placed in CSRY, ESCCNT is then decremented to 03H.

    If ESCCNT contains 03H then the character is the second parameter of the ESC,"Y" sequence and is the column coordinate. The parameter has 1FH subtracted and is placed in CSRX.

Address

@ (MSX only)

    This routine is used, by the CHGET standard routine for example, to display the cursor character when it is normally disabled. If CSRSW is non-zero the routine simply terminates with no action, otherwise the cursor is displayed (09E6H).

Address

@ (MSX only)

    This routine is used, by the CHPUT standard routine for example, to display the cursor character when it is normally enabled. If CSRSW is zero the routine simply terminates with no action. SCRMOD is checked and, if the screen is in Graphics Mode or Multicolour Mode, the routine terminates with no action. Otherwise the cursor coordinates are converted to a physical address in the VDP Name Table and the character read from that location (0BD8H) and saved in CURSAV.

    The character's eight byte pixel pattern is read from the VDP Character Pattern Table into the LINWRK buffer (0BA5H). The pixel pattern is then inverted, all eight bytes if CSTYLE indicates a block cursor, only the bottom three if CSTYLE indicates an underline cursor. The pixel pattern is copied back to the position for character code 255 in the VDP Character Pattern Table (0BBEH). The character code 255 is then placed at the current cursor location in the VDP Name Table (0BE6H) and the routine terminates.

    This method of generating the cursor character, by using character code 255, can produce curious effects under certain conditions. These can be demonstrated by executing the BASIC statement FOR N=1 TO 100: PRINT CHR$(255);:NEXT and then pressing the cursor up key.

Address

@ (MSX only)

    This routine is used, by the CHGET standard routine for example, to remove the cursor character when it is normally disabled. If CSRSW is non-zero the routine simply terminates with no action, otherwise the cursor is removed (0A33H).

Address

@ (MSX only)

    This routine is used, by the CHPUT standard routine for example, .to remove the cursor character when it is normally enabled. If CSRSW is zero the routine simply terminates with no action. .SCRMOD is checked and, if the screen is in Graphics Mode or Multicolour Mode, the routine terminates with no action. Otherwise the cursor coordinates are converted to a physical address in the VDP Name Table and the character held in CURSAV written to that location (0BE6H).

Address

@ (MSX only)

    This routine performs the ESC,"C" operation for the CHPUT standard routine control code processor. If the cursor column coordinate is already at the rightmost column, determined by LINLEN, then the routine terminates with no action. Otherwise the column coordinate is incremented and CSRX updated.

Address

@ (MSX only)

    This routine performs the BS/LEFT operation for the CHPUT standard routine control code processor. The cursor column coordinate is decremented and CSRX updated. If the column coordinate has moved beyond the leftmost position it is set to the rightmost position, from LINLEN, and an UP operation performed.

Address

@ (MSX only)

    This routine performs the ESC,"D" operation for the CHPUT standard routine control code processor. If the cursor column coordinate is already at the leftmost position then the routine terminates with no action. Otherwise the column coordinate is decremented and CSRX updated.

Address

@ (MSX only)

    This routine performs the ESC,"A" (UP) operation for the CHPUT standard routine control code processor. If the cursor row coordinate is already at the topmost position the routine terminates with no action. Otherwise the row coordinate is decremented and CSRY updated.

Address

@ (MSX only)

    This routine performs the RIGHT operation for the CHPUT standard routine control code processor. The cursor column coordinate is incremented and CSRX updated. If the column coordinate has moved beyond the rightmost position, determined by LINLEN, it is set to the leftmost position (01H) and a DOWN operation performed.

Address

@ (MSX only)

    This routine performs the ESC,"B" (DOWN) operation for the CHPUT standard routine control code processor. If the cursor row coordinate is already at the lowest position, determined by CRTCNT and CNSDFG (0C32H), then the routine terminates with no action. Otherwise the row coordinate is incremented and CSRY updated.

Address

@ (MSX only)

    This routine performs the TAB operation for the CHPUT standard routine control code processor. ASCII spaces are output (08DFH) until CSRX is a multiple of eight plus one (BIOS columns 1, 9, 17, 25, 33).

Address

@ (MSX only)

    This routine performs the ESC,"H" (HOME) operation for the CHPUT standard routine control code processor, CSRX and CSRY are simply set to 1,1. The ROM BIOS cursor coordinate system, while functionally identical to that used by the BASIC Interpreter, numbers the screen rows from 1 to 24 and the columns from 1 to 32/40.

Address

@ (MSX only)

    This routine performs the CR operation for the CHPUT standard routine control code processor, CSRX is simply set to 01H .

Address

@ (MSX only)

    This routine performs the ESC,"M" function for the CHPUT standard routine control code processor. A CR operation is first performed to set the cursor column coordinate to the leftmost position. The number of rows from the current row to the bottom of the screen is then determined, if this is zero the current row is simply erased (0AECH). The row count is first used to scroll up the relevant section of LINTTB, the line termination table, by one byte. It is then used to scroll up the relevant section of the screen a row at a time. Starting at the row below the current row, each line is copied from the VDP Name Table into the LINWRK buffer (0BAAH) then copied back to the Name Table one row higher (0BC3H). Finally the lowest row on the screen is erased (0AECH).

Address

@ (MSX only)

    This routine performs the ESC,"L" operation for the CHPDT standard routine control code processor. A CR operation is first performed to set the cursor column coordinate to the leftmost position. The number of rows from the current row to the bottom of the screen is then determined, if this is zero the current row is simply erased (0AECH). The row count is first used to scroll down the relevant section of LINTTB, the line termination table, by one byte. It is then used to scroll down the relevant section of the screen a row at a time. Starting at the next to last row of the screen, each line is copied from the VDP Name Table into the LINWRK buffer (0BAAH), then copied back to the Name Table one row lower (0BC3H). Finally the current row is erased (0AECH).

Address

@ (MSX only)

    This routine is used to perform the DEL operation for the CHPUT standard routine control code processor. A LEFT operation is first performed. If this cannot be completed, because the cursor is already at the home position, then the routine terminates with no action. Otherwise a space is written to the VDP Name Table at the cursor's physical location (0BE6H).

Address

@ (MSX only)

    This routine performs the ESC,"l" operation for the CHPUT standard routine control code processor. The cursor column coordinate is set to 01H and control drops into the ESC,"K" routine.

Address

@ (MSX only)

    This routine performs the ESC,"K" operation for the CHPHT standard routine control code processor. The row's entry in LINTTB, the line termination table, is first made non-zero to indicate that the logical line is not extended (0C29H). The cursor coordinates are converted to a physical address (0BF2H) in the VDP Name Table and the VDP set up for writes via the SETWRT standard routine. Spaces are then written directly to the VDP Data Port until the rightmost column, determined by LINLEN, is reached.

Address

@ (MSX only)

    This routine performs the ESC,"J" operation for the CHPUT standard routine control code processor. An ESC,"K" operation is performed on successive rows, starting with the current one, until the bottom of the screen is reached.

    Address ... 0B15H (from 00CCH)
    Name ...... ERAFNK (Erase Function Keys status bar)
    Input ..... None
    Exit ...... None
    Modifies .. AF, DE, EI

    Standard routine to turn the function key display off. CNSDFG is first zeroed and, if the VDP is in Graphics Mode or Multicolour Mode, the routine terminates with no further action. If the VDP is in 40x24 Text Mode or 32x24 Text Mode the last row on the screen is then erased (0AECH).

    Address ... 0B26H (from 00C9H)
    Name ...... FNKSB (Function Key Status Bar)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, EI

    Standard routine to show the function key display if it is enabled. If CNSDFG is zero the routine terminates with no action, otherwise control drops into the DSPFNK standard routine..

    Address ... 0B2BH (from 00CFH)
    Name ...... DSPFNK (Display Function Keys status bar)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, DE, EI

    Standard routine to turn the function key display on. CNSDFG is set to FFH and, if the VDP is in Graphics Mode or Multicolour Mode, the routine terminates with no further action. Otherwise the cursor row coordinate is checked and, if the cursor is on the last row of the screen, a LF code (0AH) issued to the OUTDO standard routine to scroll the screen up.

    Register pair HL is then set to point to either the unshifted or shifted function strings in the Workspace Area depending upon whether the SHIFT key is pressed. LINLEN has four subtracted, to allow a minimum of one space between fields, and is divided by five to determine the field size for each string. Successive characters are then taken from each function string, checked for graphic headers via the CNVCHR standard routine and placed in the LINWRK buffer until the string is exhausted or the zone is filled. When all five strings are completed the LINWRK buffer is written to the last row in the VDP Name Table (0BC3H).

Address

@ (MSX only)

    This routine is used by the function key display related standard routines. The contents of register A are placed in CNSDFG then SCRMOD tested and Flag NC returned if the screen is in Graphics Mode or Multicolour Mode.

Address

@ (MSX only)

    This routine copies eight bytes from the VDP VRAM into the LINWRK buffer, the VRAM physical address is supplied in register pair HL.

Address

@ (MSX only)

    This routine copies a complete row of characters, with the length determined by LINLEN, from the VDP VRAM into the LINWRK buffer. The cursor row coordinate is supplied in register L.

Address

@ (MSX only)

    This routine copies eight bytes from the LINWRK buffer into the VDP VRAM, the VRAM physical address is supplied in register pair HL.

Address

@ (MSX only)

    This routine copies a complete row of characters, with the length determined by LINLEN, from the LINWRK buffer into the VDP VRAM. The cursor row coordinate is supplied in register L.

Address

@ (MSX only)

    This routine reads a single byte from the VDP VRAM into register C. The column coordinate is supplied in register H, the row coordinate in register L.

Address

@ (MSX only)

    This routine converts a pair of screen coordinates, the column in register H and the row in register L, into a physical address in the VDP Name Table. This address is returned in register pair HL.

    The row coordinate is first multiplied by thirty-two or forty, depending upon the screen mode, and added to the column coordinate. This is then added to the Name Table base address, taken from NAMBAS, to produce an initial address.

    Because of the variable screen width, as contained in LINLEN, an additional offset has to be added to the initial address to keep the active region roughly centered within the screen. The difference between the "true" number of characters per row, thirty-two or forty, and the current width is halved and then rounded up to produce the left hand offset. For a UK machine, with a thirty-seven character width in 40x24 Text Mode, this will result in two unused characters on the left hand side and one on the right. The statement PRINT (41-WID)\2, where WID is any screen width, will display the left hand column offset in 40x24 Text Mode.

    A complete BASIC program which emulates this routine is given below:

        10 CPR=40:NAM=BASE(0):WID=PEEK(&HF3AE)
        20 SCRMD=PEEK(&HFCAF):IF SCRMD=0 THEN 40
        30 CPR=32:NAM=BASE(5):WID=PEEK(&HF3AF)
        40 LH=(CPR+1-WID)\2
        50 ADDR=NAM+(ROW-1)*CPR+(COL-1)+LH

    This program is designed for the ROW and COL coordinate system used by the ROM BIOS where home is 1,1. Line 50 may be simplified, by removing the "-1" factors, if the BASIC Interpreter's coordinate system is to be used.

Address

@ (MSX only)

    This routine calculates the address of a row's entry in LINTTB, the line termination table. The row coordinate is supplied in register L and the address returned in register pair DE.

Address

@ (MSX only)

    This routine makes a row's entry in LINTTB non-zero when entered at 0C29H and zero when entered at 0C2AH. The row coordinate is supplied in register L.

Address

@ (MSX only)

    This routine returns the number of rows on the screen in register A. It will normally return twenty-four if the function key display is disabled and twenty-three if it is enabled. Note that the screen size is determined by CRTCNT and may be modified with a BASIC statement, POKE &HF3B1H,14:SCREEN 0 for example.

    Address ... 0C3CH (from 0038H)
    Name ...... KEYINT (Keyboard Interruption handler)
    Input ..... None
    Exit ...... None
    Modifies .. EI

    Standard routine to process Z80 interrupts, these are generated by the VDP once every 1/60 s (20 ms on a UK machine). The VDP Status Register is first read and bit 7 checked to ensure that this is a frame rate interrupt, if not the routine terminates with no action. The contents of the Status Register are saved in STATFL and bit 5 checked for sprite coincidence. If the Coincidence Flag is active then the relevant entry in TRPTBL is updated (0EF1H).

    INTCNT, the "INTERVAL" counter, is then decremented. If this has reached zero the relevant entry in TRPTBL is updated (0EF1H) and the counter reset with the contents of INTVAL.

    JIFFY, the "TIME" counter, is then incremented. This counter just wraps around to zero when it overflows.

    MUSICF is examined to determine whether any of the three music queues generated by the "PLAY" statement are active. For each active queue the dequeueing routine (113BH) is called to fetch the next music packet and write it to the PSG.

    SCNCNT is then decremented to determine if a joystick and keyboard scan is required, if not the interrupt handler terminates with no further action. This counter is used to increase throughput and to minimize keybounce problems by ensuring that a scan is only carried out every three interrupts. Assuming a scan is required joystick connector 1 is selected and the two Trigger bits read (120CH), followed by the two Trigger bits from joystick connector 2 (120CH) and the SPACE key from row 8 of the keyboard (1226H). These five inputs, which are all related to the "STRIG" statement, are combined into a single byte where 0=Pressed, 1=Not pressed:

       7     6     5     4     3     2     1     0
    +-----+-----+-----+-----+-----+-----+-----+-----+
    |Joy 2|Joy 2|Joy 1|Joy 1|  0  |  0  |  0  |Space|
    |Trg.B|Trg.A|Trg.B|Trg.A|     |     |     |     |
    +-----+-----+-----+-----+-----+-----+-----+-----+

Figure 35: "STRIG" Inputs.

    This reading is compared with the previous one, held in TRGFLG, to produce an active transition byte and TRGFLG is updated with the new reading. The active transition byte is normally zero but contains a 1 in each position where a transition from unpressed to pressed has occurred. This active transition byte is shifted out bit by bit and the relevant entry in TRPTBL updated (0EF1H) for each active device.

    A complete scan of the keyboard matrix is then performed to identify new key depressions, any found are translated into key codes and placed in KEYBUF (0D12H). If KEYBUF is found to be empty at the end of this process REPCNT is decremented to see whether the auto-repeat delay has expired, if not the routine terminates. If the delay period has expired REPCNT is reset with the fast repeat value (60 ms), the OLDKEY keyboard map is reinitialized and the keyboard scanned again (0D4EH). Any keys which are continuously pressed will show up as new transitions during this scan. Note that keys will only auto-repeat while an application program keeps KEYBUF empty by reading characters. The interrupt handler then terminates.

Address

@ (MSX only)

    This routine performs a complete scan of all eleven rows of the keyboard matrix for the interrupt handler. Each of the eleven rows is read in via the PPI and placed in ascending order in NEWKEY. ENSTOP is then checked to see if warm starts are enabled. If its contents are non-zero and the keys CODE, GRAPH, CTRL and SHIFT are pressed control transfers to the BASIC Interpreter (409BH) via the CALBAS standard routine. This facility is useful as even a machine code program can be terminated as long as the interrupt handler is running. The contents of NEWKEY are compared with the previous scan contained in OLDKEY. If any change at all has occurred REPCNT is loaded with the initial auto-repeat delay (780 ms). Each row 1, reading from NEWKEY is then compared with the previous one, held in OLDKEY, to produce an active transition byte and OLDKEY is updated with the new reading. The active transition byte is normally zero but contains a 1 in each position where a transition from unpressed to pressed has occurred. If the row contains any transitions these are decoded and placed in KEYBUF as key codes (0D89H). When all eleven rows have been completed the routine checks whether there are any characters in KEYBUF, by subtracting GETPNT from PUTPNT, and terminates.

    Address ... 0D6AH (from 009CH)
    Name ...... CHSNS (Check keyboard buffer)
    Input ..... None
    Exit ...... Flag NZ if characters in KEYBUF
    Modifies .. AF, EI

    Standard routine to check if any keyboard characters are ready. If the screen is in Graphics Mode or Multicolour Mode then GETPNT is subtracted from PUTPNT (0D62H) and the routine terminates. If the screen is in 40x24 Text Mode or 32x24 Text Mode the state of the SHIFT key is also examined and the function key display updated, via the DSPFNK standard routine, if it has changed.

Address

@ (MSX only)

    This routine converts each active bit in a keyboard row transition byte into a key code. A bit is first converted into a key number determined by its position in the keyboard matrix:

    +-----+-----+-----+-----+-----+-----+-----+-----+
    |  7  |  6  |  5  |  4  |  3  |  2  |  1  |  0  |   Row 0
    |(07H)|(06H)|(05H)|(04H)|(03H)|(02H)|(01H)|(00H)|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    |  ;  |  ]  |  [  |  \  |  =  |  -  |  9  |  8  |   Row 1
    |(0FH)|(0EH)|(0DH)|(0CH)|(0BH)|(0AH)|(09H)|(08H)|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    |  B  |  A  |  £ |  /  |  .  |  ,  |  `  |  '  |   Row 2
    |(17H)|(16H)|(15H)|(14H)|(13H)|(12H)|(11H)|(10H)|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    |  J  |  I  |  H  |  G  |  F  |  E  |  D  |  C  |   Row 3
    |(1FH)|(1EH)|(1DH)|(1CH)|(1BH)|(1AH)|(19H)|(18H)|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    |  R  |  Q  |  P  |  O  |  N  |  M  |  L  |  K  |   Row 4
    |(27H)|(26H)|(25H)|(24H)|(23H)|(22H)|(21H)|(20H)|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    |  Z  |  Y  |  X  |  W  |  V  |  U  |  T  |  S  |   Row 5
    |(2FH)|(2EH)|(2DH)|(2CH)|(2BH)|(2AH)|(29H)|(28H)|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    | F3  | F2  | F1  |CODE | CAP |GRAPH|CTRL |SHIFT|   Row 6
    |(37H)|(36H)|(35H)|(34H)|(33H)|(32H)|(31H)|(30H)|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    | CR  | SEL | BS  |STOP | TAB | ESC | F5  | F4  |   Row 7
    |(3FH)|(3EH)|(3DH)|(3CH)|(3BH)|(3AH)|(39H)|(38H)|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    |RIGHT|DOWN | UP  |LEFT | DEL | INS |HOME |SPACE|   Row 8
    |(47H)|(46H)|(45H)|(44H)|(43H)|(42H)|(41H)|(40H)|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    |  4  |  3  |  2  |  1  |  0  |     |     |     |   Row 9
    |(4FH)|(4EH)|(4DH)|(4CH)|(4BH)|(4AH)|(49H)|(48H)|
    +-----+-----+-----+-----+-----+-----+-----+-----+
    |  .  |  ,  |  -  |  9  |  8  |  7  |  6  |  5  |   Row 10
    |(57H)|(56H)|(55H)|(54H)|(53H)|(52H)|(51H)|(50H)|
    +-----+-----+-----+-----+-----+-----+-----+-----+
      7     6     5     4     3     2     1     0       Column

Figure 36: Key Numbers.

    The key number is then converted into a key code and placed in KEYBUF (1021H). When all eight possible bits have been processed the routine terminates.

Address

@ (MSX only)

    This table contains the key codes of key numbers 00H to 2FH for various combinations of the control keys. A zero entry in the table means that no key code will be produced when that key is pressed:

           37H  36H  35H  34H  33H  32H  31H  30H   Row  0
           3BH  5DH  5BH  5CH  3DH  2DH  39H  38H   Row  1
    NORMAL 62H  61H  9CH  2FH  2EH  2CH  60H  27H   Row  2
           6AH  69H  68H  67H  66H  65H  64H  63H   Row  3
           72H  71H  70H  6FH  6EH  6DH  6CH  6BH   Row  4
           7AH  79H  78H  77H  76H  75H  74H  73H   Row  5

           26H  5EH  25H  24H  23H  40H  21H  29H   Row  0
           3AH  7DH  7BH  7CH  2BH  5FH  28H  2AH   Row  1
    SHIFT  42H  41H  9CH  3FH  3EH  3CH  7EH  22H   Row  2
           4AH  49H  48H  47H  46H  45H  44H  43H   Row  3
           52H  51H  50H  4FH  4EH  4DH  4CH  4BH   Row  4
           5AH  59H  58H  57H  56H  55H  54H  53H   Row  5

           FBH  F4H  BDH  EFH  BAH  ABH  ACH  09H   Row  0
           06H  0DH  01H  1EH  F1H  17H  07H  ECH   Row  1
    GRAPH  11H  C4H  9CH  1DH  F2H  F3H  BBH  05H   Row  2
           C6H  DCH  13H  15H  14H  CDH  C7H  BCH   Row  3
           18H  CCH  DBH  C2H  1BH  0BH  C8H  DDH   Row  4
           0FH  19H  1CH  CFH  1AH  C0H  12H  D2H   Row  5

           00H  F5H  00H  00H  FCH  FDH  00H  0AH   Row  0
           04H  0EH  02H  16H  F0H  1FH  08H  00H   Row  1
    SHIFT  00H  FEH  9CH  F6H  AFH  AEH  F7H  03H   Row  2
    GRAPH  CAH  DFH  D6H  10H  D4H  CEH  C1H  FAH   Row  3
           A9H  CBH  D7H  C3H  D3H  0CH  C9H  DEH   Row  4
           F8H  AAH  F9H  D0H  D5H  C5H  00H  D1H   Row  5

           E1H  E0H  98H  9BH  BFH  D9H  9FH  EBH   Row  0
           B7H  DAH  EDH  9CH  E9H  EEH  87H  E7H   Row  1
    CODE   97H  84H  9CH  A7H  A6H  86H  E5H  B9H   Row  2
           91H  A1H  B1H  81H  94H  8CH  8BH  8DH   Row  3
           93H  83H  A3H  A2H  A4H  E6H  B5H  B3H   Row  4
           85H  A0H  8AH  88H  95H  82H  96H  89H   Row  5

           00H  00H  9DH  9CH  BEH  9EH  ADH  D8H   Row  0
           B6H  EAH  E8H  00H  00H  00H  80H  E2H   Row  1
    SHIFT  00H  8EH  9CH  A8H  00H  8FH  E4H  B8H   Row  2
    CODE   92H  00H  B0H  9AH  99H  00H  00H  00H   Row  3
           00H  00H  E3H  00H  A5H  00H  B4H  B2H   Row  4
           00H  00H  00H  00H  00H  90H  00H  00H   Row  5

            7    6    5    4    3    2    1    0    Column

Address

@ (MSX only)

    Control transfers to this routine, from 0FC3H, to complete decoding of the five function keys. The relevant entry in FNKFLG is first checked to determine whether the key is associated with an "ON KEY GOSUB" statement. If so, and provided that CURLIN shows the BASIC Interpreter to be in program mode, the relevant entry in TRPTBL is updated (0EF1H) and the routine terminates. If the key is not tied to an "ON KEY GOSUB" statement, or if the Interpreter is in direct mode, the string of characters associated with the function key is returned instead. The key number is multiplied by sixteen, as each string is sixteen characters long, and added to the starting address of the function key strings in the Workspace Area. Sequential characters are then taken from the string and placed in KEYBUF (0F55H) until the zero byte terminator is reached.

Address

@ (MSX only)

    This routine is used to update a device's entry in TRPTBL when it has produced a BASIC program interrupt. On entry register pair HL points to the device's status byte in the table. Bit 0 of the status byte is checked first, if the device is not "ON" then the routine terminates with no action. Bit 2, the event flag, is then checked. If this is already set then the routine terminates, otherwise it is set to indicate that an event has occurred. Bit 1, the "STOP" flag, is then checked. If the device is stopped then the routine terminates with no further action. Otherwise ONGSBF is incremented to signal to the Interpreter Runloop that the event should now be processed.

Address

@ (MSX only)

    This section of the key decoder processes the HOME key only. The state of the SHIFT key is determined via row 6 of NEWKEY and the key code for HOME (0BH) or CLS (0CH) placed in KEYBUF (0F55H) accordingly.

Address

@ (MSX only)

    This section of the keyboard decoder processes key numbers 30H to 57H apart from the CAP, F1 to F5, STOP and HOME keys. The key number is simply used to look up the key code in the table at 1033H and this is then placed in KEYBUF (0F55H).

Address

@ (MSX only)

    This section of the keyboard decoder processes the DEAD key found on European MSX machines. On UK machines the key in row 2, column 5 always generates the pound key code (9CH) shown in the table at 0DA5H. On European machines this table will have the key code FFH in the same locations. This key code only serves as a flag to indicate that the next key pressed, if it is a vowel, should be modified to produce an accented graphics character.

    The state of the SHIFT and CODE keys is determined via row 6 of NEWKEY and one of the following placed in KANAST: 01H=DEAD, 02H=DEAD+SHIFT, 03H=DEAD+CODE, 04H=DEAD+SHIFT+CODE.

Address

@ (MSX only)

    This section of the keyboard decoder processes the CAP key. The current state of CAPST is inverted and control drops into the CHGCAP standard routine.

    Address ... 0F3DH (from 0132H)
    Name ...... CHGCAP (Change Caps Lock LED)
    Input ..... A=ON/OFF Switch
    Exit ...... None
    Modifies .. AF

    Standard routine to turn the Caps Lock LED on or off as determined by the contents of register A: 00H=On, NZ=Off. The LED is modified using the bit set/reset facility of the PPI Mode Port. As CAPST is not changed this routine does not affect the characters produced by the keyboard.

Address

@ (MSX only)

    This section of the keyboard decoder processes the STOP key. The state of the CTRL key is determined via row 6 of NEWKEY and the key code for STOP (04H) or CTRL/STOP (03H) produced as appropriate. If the CTRL/STOP code is produced it is copied to INTFLG, for use by the ISCNTC standard routine, and then placed in KEYBUF (0F55H). If the STOP code is produced it is also copied to INTFLG but is not placed in KEYBUF, instead only a click is generated (0F64H). This means that an application program cannot read the STOP key code via the ROM BIOS standard routines.

Address

@ (MSX only)

    This section of the keyboard decoder places a key code in KEYBUF and generates an audible click. The correct address in the keyboard buffer is first taken from PUTPNT and the code placed there. The address is then incremented (105BH). If it has wrapped round and caught up with GETPNT then the routine terminates with no further action as the keyboard buffer is full. Otherwise PUTPNT is updated with the new address.

    CLIKSW and CLIKFL are then both checked to determine whether a click is required. CLIKSW is a general enable/disable switch while CLIKFL is used to prevent multiple clicks when the function keys are pressed. Assuming a click is required the Key Click output is set via the PPI Mode Port and, after a delay of 50 誑, control drops into the CHGSND standard routine.

    Address ... 0F7AH (from 0135H)
    Name ...... CHGSND (Change keyboard Sound port)
    Input ..... A=ON/OFF Switch
    Exit ...... None
    Modifies .. AF

    Standard routine to set or reset the Key Click output via the PPI Mode Port: 00H=Reset, NZ=Set. This audio output is AC coupled so absolute polarities should not be taken too seriously.

Address

@ (MSX only)

    This section of the keyboard decoder processes key numbers 00H to 2FH. The state of the SHIFT, GRAPH and CODE keys is determined via row 6 of NEWKEY and combined with the key number to form a look-up address into the table at 0DA5H. The key code is then taken from the table. If it is zero the routine terminates with no further action, if it is FFH control transfers to the DEAD key processor (0F1FH). If the code is in the range 40H to 5FH or 60H to 7FH and the CTRL key is pressed then the corresponding control code is placed in KEYBUF (0F55H). If the code is in the range 01H to 1FH then a graphic header code (01H) is first placed in KEYBUF (0F55H) followed by the code with 40H added. If the code is in the range 61H to 7BH and CAPST indicates that caps lock is on then it is converted to upper case by subtracting 20H. Assuming that KANAST contains zero, as it always will on UK machines, then the key code is placed in KEYBUF (0F55H) and the routine terminates. On European MSX machines, with a DEAD key instead of a pound key, then the key codes corresponding to the vowels a, e, i, o, u may be further modified into graphics codes.

Address

@ (MSX only)

    This section of the keyboard decoder processes the five function keys. The state of the SHIFT key is examined via row 6 of NEWKEY and five added to the key number if it is pressed. Control then transfers to 0EC5H to complete processing.

Address

@ (MSX only)

    This routine searches the table at 1B97H to determine which group of keys the key number supplied in register C belongs to. The associated address is then taken from the table and control transferred to that section of the keyboard decoder. Note that the table itself is actually patched into the middle of the OUTDO standard routine as a result of the modifications made to the Japanese ROM.

Address

@ (MSX only)

    This table contains the key codes of key numbers 30H to 57H other than the special keys CAP, F1 to F5, STOP and HOME. A zero entry in the table means that no key code will be produced when that key is pressed:

           00H 00H 00H 00H 00H 00H 00H 00H Row 6
           0DH 18H 08H 00H 09H 1BH 00H 00H Row 7
           1CH 1FH 1EH 1DH 7FH 12H 0CH 20H Row 8
           34H 33H 32H 31H 30H 00H 00H 00H Row 9
           2EH 2CH 2DH 39H 38H 37H 36H 35H Row 10

            7   6   5   4   3   2   1   0  Column

Address

@ (MSX only)

    This routine simply zeroes KANAST and then transfers control to 10C2H.

Address

@ (MSX only)

    This table contains the graphics characters which replace the vowels a, e, i, o, u on European machines.

Address

@ (MSX only)

    This routine increments the keyboard buffer pointer, either PUTPNT or GETPNT, supplied in register pair HL. If the pointer then exceeds the end of the keyboard buffer it is wrapped back to the beginning.

    Address ... 10CBH (from 009FH)
    Name ...... CHGET (Character Get)
    Input ..... None
    Exit ...... A=Character from keyboard
    Modifies .. AF, EI

    Standard routine to fetch a character from the keyboard buffer. The buffer is first checked to see if already contains a character (0D6AH). If not the cursor is turned on (09DAH), the buffer checked repeatedly until a character appears (0D6AH) and then the cursor turned off (0A27H). The character is taken from the buffer using GETPNT which is then incremented (10C2H).

    Address ... 10F9H (from 00BDH)
    Name ...... CKCNTC (Check Control-stop)
    Input ..... None
    Exit ...... None
    Modifies .. AF, EI

    Standard routine to check whether the CTRL-STOP or STOP keys have been pressed. It is used by the BASIC Interpreter inside processor-intensive statements, such as "WAIT" and "CIRCLE", to check for program termination. Register pair HL is first zeroed and then control transferred to the ISCNTC standard routine. When the Interpreter is running register pair HL normally contains the address of the current character in the BASIC program text. If ISCNTC is CTRL-STOP terminated this address will be placed in OLDTXT by the "STOP" statement handler (63E6H) for use by a later "CONT" statement. Zeroing register pair HL beforehand signals to the "CONT" handler that termination occurred inside a statement and it will issue a "Can't CONTINUE" error if continuation is attempted.

    Address ... 1102H (from 0093H)
    Name ...... WRTPSG (Write to PSG register)
    Input ..... A=Register number, E=Data byte
    Exit ...... None
    Modifies .. EI

    Standard routine to write a data byte to any of the sixteen PSG registers. The register selection number is written to the PSG Address Port and the data byte written to the PSG Data Write Port.

    Address ... 110EH (from 0096H)
    Name ...... RDPSG (Read from PSG register)
    Input ..... A=Register number
    Exit ...... A=Data byte read from PSG
    Modifies .. A

    Standard routine to read a data byte from any of the sixteen PSG registers. The register selection number is written to the PSG Address Port and the data byte read from the PSG Data Read Port.

    Address ... 1113H (from 00C0H)
    Name ...... BEEP (Beep)
    Input ..... None
    Exit ...... None
    Modifies .. AF, BC, E, EI

    Standard routine to produce a beep via the PSG. Channel A is set to produce a tone of 1316 Hz then enabled with an amplitude of seven. After a delay of 40 ms control transfers to the GICINI standard routine to reinitialize the PSG.

Address

@ (MSX only)

    This routine is used by the interrupt handler to service a music queue. As there are three of these, each feeding a PSG channel, the queue to be serviced is specified by supplying its number in register A: 0=VOICAQ, 1=VOICBQ and 2=VOICCQ.

    Each string in a "PLAY" statement is translated into a series of data packets by the BASIC Interpreter. These are placed in the appropriate queue followed by an end of data byte (FFH). The task of dequeueing the packets, decoding them and setting the PSG is left to the interrupt handler. The Interpreter is thus free to proceed immediately to the next statement without having to wait for notes to finish.

    The first two bytes of any packet specify its byte count and duration. The three most significant bits of the first byte specify the number of bytes following the header in the packet. The remainder of the header specifies the event duration in 1/60 s units (20 ms in UK). This duration count determines how long it will be before the next packet is read from the queue.

       7     6     5     4     3     2     1     0
    +-----------+-----------------------------------+
    |Byte Count |           Duration (MSB)          |
    +-----------+-----------------------------------+
    |                Duration (LSB)                 |
    +-----------------------------------------------+

Figure 37: Packet Header.

    The packet header may be followed by zero or more blocks, in any order, containing frequency or amplitude information:

      7   6   5   4   3   2   1   0
    +---+---+---+---+---------------+
    | 0 | 0 | x | x |Frequency (MSB)|
    +---+---+---+---+---------------+
    |        Frequency (LSB)        |
    +-------------------------------+
    Frequency Block

      7   6   5   4   3   2   1   0
    +---+---+---+---+---+---+---+---+
    | x | 1 | x | x | x | x | x | x |
    +---+---+---+---+---+---+---+---+
    |   Envelope Frequency (MSB)    |
    +-------------------------------+
    |   Envelope Frequency (LSB)    |
    +-------------------------------+
    Envelope Block

      7    6    5    4    3    2    1    0
    +----+----+----+----+-------------------+
    | 1  | x  | x  |Mode|  Amplitude/Shape  |
    +----+----+----+----+-------------------+
    Amplitude Block

Figure 38: Packet Block Types.

    The routine first locates the current duration counter in the relevant voice buffer (VCBA, VCBB or VCBC) via the GETVCP standard routine and decrements it. If the counter has reached zero then the next packet must be read from the queue, otherwise the routine terminates.

    The queue number is placed in QUEUEN and a byte read from the queue (11E2H). This is then checked to see if it is the end of data mark (FFH), if so the queue terminates (11B0H). Otherwise the byte count is placed in register C and the duration MSB in the relevant voice buffer. The second byte is read (11E2H) and the duration LSB placed in the relevant voice buffer. The byte count is then examined, if there are no bytes to follow the packet header the routine terminates. Otherwise successive bytes are read from the queue, and the appropriate action taken, until the byte count is exhausted.

    If a frequency block is found then a second byte is read and both bytes written to PSG Registers 0 and 1, 2 and 3 or 4 and 5 depending on the queue number.

    If an amplitude block is found the Amplitude and Mode bits are written to PSG Registers 8, 9 or 10 depending on the queue number. If the Mode bit is 1, selecting modulated rather than fixed amplitude, then the byte is also written to PSG Register 13 to set the envelope shape.

    If an envelope block is found, or if bit 6 of an amplitude block is set, then a further two bytes are read from the queue and written to PSG Registers 11 and 12.

Address

@ (MSX only)

    This routine is used when an end of data mark (FFH) is found in one of the three music queues. An amplitude value of zero is written to PSG Register 8 9 or 10, depending on the queue number, to shut the channel down. The channel's bit in MUSICF is then reset and control drops into the STRTMS standard routine.

    Address ... 11C4H (from 0099H)
    Name ...... STRTMS (Start Music)
    Input ..... None
    Exit ...... None
    Modifies .. AF, HL

    Standard routine used by the "PLAY" statement handler to initiate music dequeueing by the interrupt handler. MUSICF is first examined, if any channels are already running the routine terminates with no action. PLYCNT is then decremented, if there are no more "PLAY" strings queued up the routine terminates. Otherwise the three duration counters, in VCBA, VCBB and VCBC, are set to 0001H, so that the first packet of the new group will be dequeued at the next interrupt, and MUSICF is set to 07H to enable all three channels.

Address

@ (MSX only)

    This routine loads register A with the current queue number, from QUEUEN, and then reads a byte from that queue (14ADH).

    Address ... 11EEH (from 00D5H)
    Name ...... GTSTCK (Get joyStick status)
    Input ..... A=Joystick ID (0, 1 or 2)
    Exit ...... A=Joystick position code
    Modifies .. AF, B, DE, HL, EI

    Standard routine to read the position of a joystick or the four cursor keys. If the supplied ID is zero the state of the cursor keys is read via PPI Port B (1226H) and converted to a position code using the look-up table at 1243H. Otherwise joystick connector 1 or 2 is read (120CH) and the four direction bits converted to a position code using the look-up table at 1233H. The returned position codes are:

             1
          8  |  2
           \ | /
            \|/
        7----0----3
            /|\
           / | \
          6  |  4
             5

Address

@ (MSX only)

    This routine reads the joystick connector specified by the contents of register A: 0=Connector 1, 1=Connector 2. The current contents of PSG Register 15 are read in then written back with the Joystick Select bit appropriately set. PSG Register 14 is then read into register A (110CH) and the routine terminates.

Address

@ (MSX only)

    This routine reads row 8 of the keyboard matrix. The current contents of PPI Port C are read in then written back with the four Keyboard Row Select bits set for row 8. The column inputs are then read into register A from PPI Port B.

    Address ... 1253H (from 00D8H)
    Name ...... GTTRIG (Get Trigget status)
    Input ..... A=Trigger ID (0, 1, 2, 3 or 4)
    Exit ...... A=Status code
    Modifies .. AF, BC, EI

    Standard routine to check the joystick trigger or space key status. If the supplied ID is zero row 8 of the keyboard matrix is read (1226H) and converted to a status code. Otherwise joystick connector 1 or 2 is read (120CH) and converted to a status code. The selection IDs are:

0=SPACE KEY
1=JOY 1, TRIGGER A
2=JOY 2, TRIGGER A
3=JOY 1, TRIGGER B
4=JOY 2, TRIGGER B

    The value returned is FFH if the relevant trigger is pressed and zero otherwise.

    Address ... 1273H (from 00DEH)
    Name ...... GTPDL (Get Paddle status)
    Input ..... A=Paddle ID (1 to 12)
    Exit ...... A=Paddle value (0 to 255)
    Modifies .. AF, BC, DE, EI

    Standard routine to read the value of any paddle attached to a joystick connector. Each of the six input lines (four direction plus two triggers) per connector can support a paddle so twelve are possible altogether. The paddles attached to joystick connector 1 have entry identifiers 1, 3, 5, 7, 9 and 11. Those attached to joystick connector 2 have entry identifiers 2, 4, 6, 8, 10 and 12. Each paddle is basically a one-shot pulse generator, the length of the pulse being controlled by a variable resistor. A start pulse is issued to the specified joystick connector via PSG Register 15. A count is then kept of how many times PSG Register 14 has to be read until the relevant input times out. Each unit increment represents an approximate period of 12 誑 on an MSX machine with one wait state.

    Address ... 12ACH (from 00DBH)
    Name ...... GTPAD (Get touchPad status)
    Input ..... A=Function code (0 to 7)
    Exit ...... A=Status or value
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to access a touchpad attached to either of the joystick connectors. Available functions codes for joystick connector 1 are:

0 = Return Activity Status
1 = Return "X" coordinate
2 = Return "Y" coordinate
3 = Return Switch Status

    Function codes 4 to 7 have the same effect with respect to joystick connector 2. The Activity Status function returns FFH if the Touchpad is being touched and zero otherwise. The Switch Status function returns FFH if the switch is being pressed and zero otherwise. The two coordinate request functions return the coordinates of the last location touched. These coordinates are actually stored in the Workspace Area variables PADX and PADY when a call with function code 0 or 4 detects activity. Note that these variables are shared by both joystick connectors.

    Address ... 1384H (from 00F3H)
    Name ...... STMOTR (Set Motor)
    Input ..... A=Motor ON/OFF code
    Exit ...... None
    Modifies .. AF

    Standard routine to turn the cassette motor relay on or off via PPI Port C: 00H=Off, 01H=On, FFH=Reverse current state. * Note: doesn't work with turbo R.

    Address ... 1398H (from 0066H)
    Name ...... NMI (Non-Maskable Interruption handler)
    Input ..... None
    Exit ...... None
    Modifies .. None

    Standard routine to process a Z80 Non Maskable Interrupt, simply returns on a standard MSX machine.

    Address ... 139DH (from 003EH)
    Name ...... INIFNK (Initialize Function Key strings)
    Input ..... None
    Exit ...... None
    Modifies .. BC, DE, HL

    Standard routine to initialize the ten function key strings to their power-up values. The one hundred and sixty bytes of data commencing at 13A9H are copied to the FNKSTR buffer in the Workspace Area.

Address

@ (MSX only)

    This area contains the power-up strings for the ten function keys. They may change depending on the maker and the MSX version. Each string is sixteen characters long, unused positions contain zeroes:

        F1 to F5  F6 to F10
        color     color 15,4,4 CR
        auto      cload"
        goto      cont CR
        list      list. CR UP UP
        run CR    run CLS CR

    Address ... 1449H (from 013EH)
    Name ...... RDVDP (Read VDP status register)
    Input ..... None
    Exit ...... A=VDP Status Register contents
    Modifies .. A

    Standard routine to input the contents of the VDP Status Register by reading the Command Port. Note that reading the VDP Status Register will clear the associated flags and may affect the interrupt handler.

    Address ... 144CH (from 0138H)
    Name ...... RSLREG (Read from primary Slot Register)
    Input ..... None
    Exit ...... A=Primary Slot Register contents
    Modifies .. A

    Standard routine to input the contents of the Primary slot Register by reading PPI Port A.

    Address ... 144FH (from 013BH)
    Name ...... WSLREG (Write to primary Slot Register)
    Input ..... A=Value to write
    Exit ...... None
    Modifies .. None

    Standard routine to set the Primary Slot Register by writing to PPI Port A.

    Address ... 1452H (from 0141H)
    Name ...... SNSMAT (read keyboard Matrix row)
    Input ..... A=Keyboard row number
    Exit ...... A=Column data of keyboard row
    Modifies .. AF, C, EI

    Standard routine to read a complete row of the keyboard matrix. PPI Port C is read in then written back with the row number occupying the four Keyboard Row Select bits. PPI Port B is then read into register A to return the eight column inputs. The four miscellaneous control outputs of PPI Port C are unaffected by this routine.

    Address ... 145FH (from 014AH)
    Name ...... ISFLIO (Is File I/O)
    Input ..... None
    Exit ...... Flag NZ if file I/O active
    Modifies .. AF

    Standard routine to check whether the BASIC Interpreter is currently directing its input or output via an I/O buffer. This is determined by examining PTRFIL. It is normally zero but will contain a buffer FCB (File Control Block) address while statements such as "PRINT#1", "INPUT#1", etc. are being executed by the Interpreter.

    Address ... 146AH (from 0020H)
    Name ...... DCOMPR (16 bit Data Compare)
    Input ..... HL, DE
    Exit ...... Flag NC if HL>DE, Flag Z if HL=DE, Flag C if HL<DE
    Modifies .. AF

    Standard routine used by the BASIC Interpreter to check the relative values of register pairs HL and DE.

    Address ... 1470H (from 0150H)
    Name ...... GETVCP (Get Voice Pointer)
    Input ..... A=Voice number (0, 1, 2)
    Exit ...... HL=Address in voice buffer
    Modifies .. AF, HL

    Standard routine to return the address of byte 2 in the specified voice buffer (VCBA, VCBB or VCBC).

    Address ... 1474H (from 0153H)
    Name ...... GETVC2 (Get Voice pointer 2)
    Input ..... L=Byte number (0 to 36)
    Exit ...... HL=Address in voice buffer
    Modifies .. AF, HL

    Standard routine to return the address of any byte in the voice buffer (VCBA, VCBB or VCBC) specified by the voice number in VOICEN.

    Address ... 148AH (from 0144H)
    Name ...... PHYDIO (Physical Disk I/O access)
    Input ..... None
    Exit ...... None
    Modifies .. None

    Standard routine for use by Disk BASIC, simply returns on standard MSX machines.

    Address ... 148EH (from 0147H)
    Name ...... FORMAT (Format disk)
    Input ..... None
    Exit ...... None
    Modifies .. None

    Standard routine for use by Disk BASIC, simply returns on standard MSX machines.

    Address ... 1492H (from 00F9H)
    Name ...... PUTQ (Put byte in Queue)
    Input ..... A=Queue number, E=Data byte
    Exit ...... Flag Z if queue full
    Modifies .. AF, BC, HL

    Standard routine to place a data byte in one of the three music queues. The queue's get and put positions are first taken from QUETAB (14FAH). The put position is temporarily incremented and compared with the get position, if they are equal the routine terminates as the queue is full. Otherwise the queue's address is taken from QUETAB and the put position added to it. The data byte is placed at this location in the queue, the put position is incremented and the routine terminates. Note that the music queues are circular, if the get or put pointers reach the last position in the queue they wrap around back to the start.

Address

@ (MSX only)

    This routine is used by the interrupt handler to read a byte from one of the three music queues. The queue number is supplied in register A, the data byte is returned in register A and the routine returns Flag Z if the queue is empty. The queue's get and put positions are first taken from QUETAB (14FAH). If the putback flag is active then the data byte is taken from QUEBAK and the routine terminates (14D1H), this facility is unused in the current versions of the MSX ROM. The put position is then compared with the get position, if they are equal the routine terminates as the queue is empty. Otherwise the queue's address is taken from QUETAB and the get position added to it. The data byte is read from this location in the queue, the get position is incremented and the routine terminates.

Address

@ (MSX only)

    This routine is used by the GICINI standard routine to initialize a queue's control block in QUETAB. The control block is first located in QUETAB (1504H) and the put, get and putback bytes zeroed. The size byte is set from register B and the queue address from register pair DE.

    Address ... 14EBH (from 00F6H)
    Name ...... LFTQ (space Left in Queue)
    Input ..... A=Queue number
    Exit ...... HL=Free space left in queue
    Modifies .. AF, BC, HL

    Standard routine to return the number of free bytes left in a music queue. The queue's get and put positions are taken from QUETAB (14FAH) and the free space determined by subtracting put from get.

Address

@ (MSX only)

    This routine returns a queue's control parameters from QUETAB, the queue number is supplied in register A. The control block is first located in QUETAB (1504H), the put position is then placed in register B, the get position in register C and the putback flag in register A.

Address

@ (MSX only)

    This routine locates a queue's control block in QUETAB. The queue number is supplied in register A and the control block address returned in register pair HL. The queue number is simply multiplied by six, as there are six bytes per block, and added to the address of QUETAB as held in QUEUES.

    Address ... 1510H (from 008DH)
    Name ...... GRPPRT (Graphical mode Print)
    Input ..... A=Character
    Exit ...... None
    Modifies .. EI

    Standard routine to display a character on the screen in either Graphics Mode or Multicolour Mode, it is functionally equivalent to the CHPUT standard routine.

    The CNVCHR standard routine is first used to check for a graphic character, if the character is a header code (01H) then the routine terminates with no action. If the character is a converted graphic one then the control code decoding section is skipped. Otherwise the character is checked to see if it is a control code. Only the CR code (0DH) is recognized (157EH), all other characters smaller than 20H are ignored.

    Assuming the character is displayable its eight byte pixel pattern is copied from the ROM character set into the PATWRK buffer (0752H) and FORCLR copied to ATRBYT to set its colour. The current graphics coordinates are then taken from GRPACX and GRPACY and used to set the current pixel physical address via the SCALXY and MAPXYC standard routines.

    The eight byte pattern in PATWRK is processed a byte at a time. At the start of each byte the current pixel physical address is obtained via the FETCHC standard routine and saved. The eight bits are then examined in turn. If the bit is a 1 the associated pixel is set by the SETC standard routine, if it is a 0 no action is taken. After each bit the current pixel physical address is moved right (16ACH). When the byte is finished, or the right hand edge of the screen is reached, the initial current pixel physical address is restored and moved down one position by the TDOWNC standard routine.

    When the pattern is complete, or the bottom of the screen has been reached, GRPACX is updated. In Graphics Mode its value is increased by eight, in Multicolour Mode by thirty-two. If GRPACX then exceeds 255, the right hand edge of the screen, a CR operation is performed (157EH).

Address

@ (MSX only)

    This routine performs the CR operation for the GRPPRT standard routine, this code functions as a combined CR,LF. GRPACX is zeroed and eight or thirty-two, depending on the screen mode, added to GRPACY. If GRPACY then exceeds 191, the bottom of the screen, it is set to zero.

    GRPACX and GRPACY may be manipulated directly by an application program to compensate for the limited number of control functions available.

    Address ... 1599H (from 010EH)
    Name ...... SCALXY (Scale (X,Y) coordinates)
    Input ..... BC=X coordinate, DE=Y coordinate
    Exit ...... Flag NC if clipped
    Modifies .. AF

    Standard routine to clip a pair of graphics coordinates if necessary. The BASIC Interpreter can produce coordinates in the range -32768 to +32767 even though this far exceeds the actual screen size. This routine modifies excessive coordinate values to fit within the physically realizable range. If the X coordinate is greater than 255 it is set to 255, if the Y coordinate is greater than 191 it is set to 191. If either coordinate is negative (greater than 7FFFH) it is set to zero. Finally if the screen is in Multicolour Mode both coordinates are divided by four as required by the MAPXYC standard routine.

Address

@ (MSX only)

    This routine is used to check the current screen mode, it returns Flag Z if the screen is in Graphics Mode.

    Address ... 15DFH (from 0111H)
    Name ...... MAPXYC (Map (X,Y) Coordinate)
    Input ..... BC=X coordinate, DE=Y coordinate
    Exit ...... None
    Modifies .. AF, D, HL

    Standard routine to convert a graphics coordinate pair into the current pixel physical address. The location in the Character Pattern Table of the byte containing the pixel is placed in CLOC. The bit mask identifying the pixel within that byte is placed in CMASK. Slightly different conversion methods are used for Graphics Mode and Multicolour Mode, equivalent programs in BASIC are:

        Graphics Mode

        10 INPUT"X,Y Coordinates";X,Y
        20 A=(Y\8)*256+(Y AND 7)+(X AND &HF8)
        30 PRINT"ADDR=";HEX$(Base(12)+A);"H ";
        40 RESTORE 100
        50 FOR N=0 TO (X AND 7):READ M$: NEXT N
        60 PRINT"MASK=";M$
        70 GOTO 10
        100 DATA 10000000
        110 DATA 01000000
        120 DATA 00100000
        130 DATA 00010000
        140 DATA 00001000
        150 DATA 00000100
        160 DATA 00000010
        170 DATA 00000001

Multicolour Mode

10 INPUT"X,Y Coordinates";X,Y
20 X=X\4:Y-Y\4
30 A=(Y\8)*256+(Y AND 7)+(X*4 AND &HF8)
40 PRINT"ADDR=";HEX$(BASE(17)+A);"H ";
50 IF X MOD 2=0 THEN MS="11110000" ELSE MS="00001111"
60 PRINT"MASK=";M$
70 GOTO 10


    The allowable input range for both programs is X=0 to 255 and Y=0 to 191. The data statements in the Graphics Mode program correspond to the eight byte mask table commencing at 160BH in the MSX ROM. Line 20 in the Multicolour Mode program actually corresponds to the division by four in the SCALXY standard routine. It is included to make the coordinate system consistent for both programs.

    Address ... 1639H (from 0114H)
    Name ...... FETCHC (Fetch Coordinate)
    Input ..... None
    Exit ...... A=CMASK, HL=CLOC
    Modifies .. A, HL

    Standard routine to return the current pixel physical address, register pair HL is loaded from CLOC and register A from CMASK.

    Address ... 1640H (from 0117H)
    Name ...... STOREC (Store Coordinate)
    Input ..... A=CMASK, HL=CLOC
    Exit ...... None
    Modifies .. None

    Standard routine to set the current pixel physical address, register pair HL is copied to CLOC and register A is copied to CMASK.

    Address ... 1647H (from 011DH)
    Name ...... READC (Read current pixel Colour)
    Input ..... None
    Exit ...... A=Colour code of current pixel
    Modifies .. AF, EI

    Standard routine to return the colour of the current pixel. The VRAM physical address is first obtained via the FETCHC standard routine. If the screen is in Graphics Mode the byte pointed to by CLOC is read from the Character Pattern Table via the RDVRM standard routine. The required bit is then isolated by CMASK and used to select either the upper or lower four bits of the corresponding entry in the Colour Table.

    If the screen is in Multicolour Mode the byte pointed to by CLOC is read from the Character Pattern Table via the RDVRM standard routine. CMASK is then used to select either the upper or lower four bits of this byte. The value returned in either case will be a normal VDP colour code from zero to fifteen.

    Address ... 1676H (from 011AH)
    Name ...... SETATR (Set Attribute)
    Input ..... A=Colour code
    Exit ...... Flag C if illegal code
    Modifies .. Flags

    Standard routine to set the graphics ink colour used by the SETC and NSETCX standard routines. The colour code, from zero to fifteen, is simply placed in ATRBYT.

    Address ... 167EH (from 0120H)
    Name ...... SETC (Set current pixel Colour)
    Input ..... None
    Exit ...... None
    Modifies .. AF, EI

    Standard routine to set the current pixel to any colour, the colour code is taken from ATRBYT. The pixel's VRAM physical address is first obtained via the FETCHC standard routine. In Graphics Mode both the Character Pattern Table and Colour Table are then modified (186CH).

    In Multicolour Mode the byte pointed to by CLOC is read from the Character Pattern Table by the RDVRM standard routine. The contents of ATRBYT are then placed in the upper or lower four bits, as determined by CMASK, and the byte written back via the WRTVRM standard routine.

Address

@ (MSX only)

    This routine moves the current pixel physical address one position right. If the right hand edge of the screen is exceeded it returns with Flag C and the physical address is unchanged. In Graphics Mode CMASK is first shifted one bit right, if the pixel still remains within the byte the routine terminates. If CLOC is at the rightmost character cell (LSB=F8H to FFH) then the routine terminates with Flag C (175AH). Otherwise CMASK is set to 80H, the leftmost pixel, and 0008H added to CLOC.

    In Multicolour Mode control transfers to a separate routine (1779H).

    Address ... 16C5H (from 00FCH)
    Name ...... RIGHTC (Move Right Coordinate)
    Input ..... None
    Exit ...... None
    Modifies .. AF

    Standard routine to move the current pixel physical address one position right. In Graphics Mode CMASK is first shifted one bit right, if the pixel still remains within the byte the routine terminates. Otherwise CMASK is set to 80H, the leftmost pixel, and 0008H added to CLOC. Note that incorrect addresses will be produced if the right hand edge of the screen is exceeded.

    In Multicolour Mode control transfers to a separate routine (178BH).

Address

@ (MSX only)

    This routine moves the current pixel physical address one position left. If the left hand edge of the screen is exceeded it returns Flag C and the physical address is unchanged. In Graphics Mode CMASK is first shifted one bit left, if the pixel still remains within the byte the routine terminates. If CLOC is at the leftmost character cell (LSB=00H to 07H) then the routine terminates with Flag C (175AH). Otherwise CMASK is set to 01H, the rightmost pixel, and 0008H subtracted from CLOC.

    In Multicolour Mode control transfers to a separate routine (179CH).

    Address ... 16EEH (from 00FFH)
    Name ...... LEFTC (move Left Coordinate)
    Input ..... None
    Exit ...... None
    Modifies .. AF

    Standard routine to move the current pixel physical address one position left. In Graphics Mode CMASK is first shifted one bit left, if the pixel still remains within the byte the routine terminates. Otherwise CMASK is set to 01H, the leftmost pixel, and 0008H subtracted from CLOC. Note that incorrect addresses will be produced if the left hand edge of the screen is exceeded.

    In Multicolour Mode control transfers to a separate routine (17ACH).

    Address ... 170AH (from 010BH)
    Name ...... TDOWNC (Test and move Down Coordinate)
    Input ..... None
    Exit ...... Flag C if off screen
    Modifies .. AF

    Standard routine to move the current pixel physical address one position down. If the bottom edge of the screen is exceeded it returns Flag C and the physical address is unchanged. In Graphics Mode CLOC is first incremented, if it still remains within an eight byte boundary the routine terminates. If CLOC was in the bottom character row (CLOC>=1700H) then the routine terminates with Flag C (1759H). Otherwise 00F8H is added to CLOC.

    In Multicolour Mode control transfers to a separate routine (17C6H).

    Address ... 172AH (from 0108H)
    Name ...... DOWNC (move Down Coordinate)
    Input ..... None
    Exit ...... None
    Modifies .. AF

    Standard routine to move the current pixel physical address one position down. In Graphics Mode CLOC is first incremented, if it still remains within an eight byte boundary the routine terminates. Otherwise 00F8H is added to CLOC. Note that incorrect addresses will be produced if the bottom edge of the screen is exceeded.

    In Multicolour Mode control transfers to a separate routine (17DCH).

    Address ... 173CH (from 0105H)
    Name ...... TUPC (Test and move Up Coordinate)
    Input ..... None
    Exit ...... Flag C if off screen
    Modifies .. AF

    Standard routine to move the current pixel physical address one position up. If the top edge of the screen is exceeded it returns with Flag C and the physical address is unchanged. In Graphics Mode CLOC is first decremented, if it still remains within an eight byte boundary the routine terminates. If CLOC was in the top character row (CLOC<0100H) then the routine terminates with Flag C. Otherwise 00F8H is subtracted from CLOC.

    In Multicolour Mode control transfers to a separate routine (17E3H).

    Address ... 175DH (from 0102H)
    Name ...... UPC (move Up Coordinate)
    Input ..... None
    Exit ...... None
    Modifies .. AF

    Standard routine to move the current pixel physical address one position up. In Graphics Mode CLOC is first decremented, if it still remains within an eight byte boundary the routine terminates. Otherwise 00F8H is subtracted from CLOC. Note that incorrect addresses will be produced if the top edge of the screen is exceeded.

    In Multicolour Mode control transfers to a separate routine (17F8H). - 74 - 4. ROM BIOS Address ... 1779H

Address

@ (MSX only)

    This is the Multicolour Mode version of the routine at 16ACH. It is identical to the Graphics Mode version except that CMASK is shifted four bit positions right and becomes F0H if a cell boundary is crossed. Address ... 178BH

Address

@ (MSX only)

    This is the Multicolour Mode version of the RIGHTC standard routine. It is identical to the Graphics Mode version except that CMASK is shifted four bit positions right and becomes F0H if a cell boundary is crossed. Address ... 179CH

Address

@ (MSX only)

    This is the Multicolour Mode version of the routine at 16D8H. It is identical to the Graphics Mode version except that CMASK is shifted four bit positions left and becomes 0FH if a cell boundary is crossed. Address ... 17ACH

Address

@ (MSX only)

    This is the Multicolour Mode version of the LEFTC standard routine. It is identical to the Graphics Mode version except that CMASK is shifted four bit positions left and becomes 0FH if a cell boundary is crossed. Address ... 17C6H

Address

@ (MSX only)

    This is the Multicolour Mode version of the TDOWNC standard routine. It is identical to the Graphics Mode version except that the bottom boundary address is 0500H instead of 1700H. There is a bug in this routine which will cause it to behave unpredictably if MLTCGP, the Character Pattern Table base address, is changed from its normal value of zero. There should be an EX DE,HL instruction inserted at address 17CEH.

    If the Character Pattern Table base is increased the routine will think it has reached the bottom of the screen when it actually has not. This routine is used by the "PAINT" statement so the following demonstrates the fault:

        10 BASE(17)=&H1000
        20 SCREEN 3
        30 PSET(200,0)
        40 DRAW"D180L100U180R100"
        50 PAINT(150,90)
        60 GOTO 60

Address

@ (MSX only)

    This is the Multicolour Mode version of the DOWNC standard routine, it is identical to the Graphics Mode version. - 75 - 4. ROM BIOS Address ... 17E3H

Address

@ (MSX only)

    This is the Multicolour Mode version of the TUPC standard routine. It is identical to the Graphics Mode version except that is has a bug as above, this time there should be an EX DE,HL instruction at address 17EBH.

    If the Character Pattern Table base address is increased the routine will think it is within the table when it has actually exceeded the top edge of the screen. This may be demonstrated by removing the "R100" part of Line 40 in the previous program. Address ... 17F8H

Address

@ (MSX only)

    This is the Multicolour Mode version of the UPC standard routine, it is identical to the Graphics Mode version.

    Address ... 1809H (from 0123H)
    Name ...... NSETCX (N [multiple] Set pixel Colour X [right])
    Input ..... HL=Pixel fill count
    Exit ...... None
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to set the colour of multiple pixels horizontally rightwards from the current pixel physical address. Although its function can be duplicated by the SETC and RIGHTC standard routines this would result in significantly slower operation. The supplied pixel count should be chosen so that the right-hand edge of the screen is not passed as this will produce anomalous behaviour. The current pixel physical address is unchanged by this routine.

    In Graphics Mode CMASK is first examined to determine the number of pixels to the right within the current character cell. Assuming the fill count is large enough these are then set (186CH). The remaining fill count is divided by eight to determine the number of whole character cells. Successive bytes in the Character Pattern Table are then zeroed and the corresponding bytes in the Colour Table set from ATRBYT to fill these whole cells. The remaining fill count is then converted to a bit mask, using the seven byte table at 185DH, and these pixels are set (186CH).

    In Multicolour Mode control transfers to a separate routine (18BBH). Address ... 186CH

Address

@ (MSX only)

    This routine sets up to eight pixels within a cell to a specified colour in Graphics Mode. ATRBYT contains the colour code, register pair HL the address of the relevant byte in the Character Pattern Table and register A a bit mask, 11100000 for example, where every 1 specifies a bit to be set. - 76 - 4. ROM BIOS

    If ATRBYT matches the existing 1 pixel colour in the corresponding Colour Table byte then each specified bit is set to 1 in the Character Pattern Table byte. If ATRBYT matches the existing 0 pixel colour in the corresponding Colour Table byte then each specified bit is set to 0 in the Character Pattern Table byte.

    If ATRBYT does not match either of the existing colours in the Colour Table Byte then normally each specified bit is set to 1 in the Character Pattern Table byte and the 1 pixel colour changed in the Colour Table byte. However if this would result in all bits being set to 1 in the Character Pattern Table byte then each specified bit is set to 0 and the 0 pixel colour changed in the Colour Table byte. Address ... 18BBH

Address

@ (MSX only)

    This is the Multicolour Mode version of the NSETCX standard routine. The SETC and RIGHTC standard routines are called until the fill count is exhausted. Speed of operation is not so important in Multicolour Mode because of the lower screen resolution and the consequent reduction in the number of operations required.

    Address ... 18C7H (from 0126H)
    Name ...... GTASPC (Get circle Aspect)
    Input ..... None
    Exit ...... DE=ASPCT1, HL=ASPCT2
    Modifies .. DE, HL

    Standard routine to return the "CIRCLE" statement default aspect ratios.

    Address ... 18CFH (from 0129H)
    Name ...... PNTINI (Paint Initialization)
    Input ..... A=Boundary colour (0 to 15)
    Exit ...... Flag C if illegal colour
    Modifies .. AF

    Standard routine to set the boundary colour for the "PAINT" statement. In Multicolour Mode the supplied colour code is placed in BDRATR. In Graphics Mode BDRATR is copied from ATRBYT as it is not possible to have separate paint and boundary colours.

    Address ... 18E4H (from 012CH)
    Name ...... SCANR (Scan Right)
    Input ..... B=Fill switch, DE=Skip count
    Exit ...... DE=Skip remainder, HL=Pixel count
    Modifies .. AF, BC, DE, HL, EI

    Standard routine used by the "PAINT" statement handler to search rightwards from the current pixel physical address until a colour code equal to BDRATR is found or the edge of the screen is reached. The terminating position becomes the current pixel physical address and the initial position is returned in CSAVEA and CSAVEM. The size of the traversed region is returned in register pair HL and FILNAM+1. The traversed region is normally filled in but this can be inhibited, in Graphics Mode only, by using an entry parameter of zero in register B. The skip count in register pair DE determines the maximum number of pixels of the required colour that may be ignored from the initial starting position. This facility is used by the "PAINT" statement handler to search for gaps in a horizontal boundary blocking its upward progress.

    Address ... 197AH (from 012FH)
    Name ...... SCANL (Scan Left)
    Input ..... None
    Exit ...... HL=Pixel count
    Modifies .. AF, BC, DE, HL, EI

    Standard routine to search leftwards from the current pixel physical address until a colour code equal to BDRATR is found or the edge of the screen is reached. The terminating position becomes the current pixel physical address and the size of the traversed region is returned in register pair HL. The traversed region is always filled in. Address ... 19C7H

Address

@ (MSX only)

    This routine is used by the SCANL and SCANR standard routines to check the current pixel's colour against the boundary colour in BDRATR.

    Address ... 19DDH (from 00F0H)
    Name ...... TAPOOF (Tape Output Off)
    Input ..... None
    Exit ...... None
    Modifies .. EI

    Standard routine to stop the cassette motor after data has been written to the cassette. After a delay of 550 ms, on MSX machines with one wait state, control drops into the TAPIOF standard routine.

    Address ... 19E9H (from 00E7H)
    Name ...... TAPIOF (Tape Input Off)
    Input ..... None
    Exit ...... None
    Modifies .. EI

    Standard routine to stop the cassette motor after data has been read from the cassette. The motor relay is opened via the PPI Mode Port. Note that interrupts, which must be disabled during cassette data transfers for timing reasons, are enabled as this routine terminates. - 78 - 4. ROM BIOS

    Address ... 19F1H (from 00EAH)
    Name ...... TAPOON (Tape Output On)
    Input ..... A=Header length switch
    Exit ...... Flag C if CTRL-STOP termination
    Modifies .. AF, BC, HL, DI

    Standard routine to turn the cassette motor on, wait 550 ms for the tape to come up to speed and then write a header to the cassette. A header is a burst of HI cycles written in front of every data block so the baud rate can be determined when the data is read back.

    The length of the header is determined by the contents of register A: 00H=Short header, NZ=Long header. The BASIC cassette statements "SAVE", "CSAVE" and "BSAVE" all generate a long header at the start of the file, in front of the identification block, and thereafter use short headers between data blocks. The number of cycles in the header is also modified by the current baud rate so as to keep its duration constant:

        1200 Baud SHORT ... 3840 Cycles ... 1.5 Seconds
        1200 Baud LONG ... 15360 Cycles ... 6.1 Seconds
        2400 Baud SHORT ... 7936 Cycles ... 1.6 Seconds
        2400 Baud LONG ... 31744 Cycles ... 6.3 Seconds

    After the motor has been turned on and the delay has expired the contents of HEADER are multiplied by two hundred and fifty- six and, if register A is non-zero, by a further factor of four to produce the cycle count. HI cycles are then generated (1A4DH) until the count is exhausted whereupon control transfers to the BREAKX standard routine. Because the CTRL-STOP key is only examined at termination it is impossible to break out part way through this routine.

    Address ... 1A19H (from 00EDH)
    Name ...... TAPOUT (Tape Output)
    Input ..... A=Data byte
    Exit ...... Flag C if CTRL-STOP termination
    Modifies .. AF, B, HL

    Standard routine to write a single byte of data to the cassette. The MSX ROM uses a software driven FSK (Frequency Shift Keyed) method for storing information on the cassette. At the 1200 baud rate this is identical to the Kansas City Standard used by the BBC for the distribution of BASICODE programs.

    At 1200 baud each 0 bit is written as one complete 1200 Hz LO cycle and each 1 bit as two complete 2400 Hz HI cycles. The data rate is thus constant as 0 and 1 bits have the same duration. When the 2400 baud rate is selected the two frequencies change to 2400 Hz and 4800 Hz but the format is otherwise unchanged. - 79 - 4. ROM BIOS

    A byte of data is written with a 0 start bit (1A50H), eight data bits with the least significant bit first, and two 1 stop bits (1A40H). At the 1200 baud rate a single byte will have a nominal duration of 11 x 833 誑 = 9.2 ms. After the stop bits have been written control transfers to the BREAKX standard routine to check the CTRL-STOP key. The byte 43H is shown below as it would be written to cassette:

      +-+++++++++ +-+ +-+ +-+ +-+++++ +-+++++++++
      | ||||||||| | | | | | | | ||||| | |||||||||
    --+ +++++++++-+ +-+ +-+ +-+ +++++-+ +++++++++
    |   |   |   |   |   |   |   |   |   |   |   |
    START 0   1   2   3   4   5   6   7 STOP STOP

    1 = two "short" transitions (as STOP BITS)
    0 = one "long" transition (as START BIT)

Figure 39: Cassette Data Byte.

    It is important not to leave too long an interval between bytes when writing data as this will increase the error rate. An inter-byte gap of 80 誑, for example, produces a read failure rate of approximately twelve percent. If a substantial amount of processing is required between each byte then buffering should be used to lump data into headered blocks. The BASIC "SAVE" format is of this type. Address ... 1A39H

Address

@ (MSX only)

    This routine writes a single LO cycle with a length of approximately 816 誑 to the cassette. The length of each half of the cycle is taken from LOW and control transfers to the general cycle generator (1A50H). Address ... 1A40H

Address

@ (MSX only)

    This routine writes two HI cycles to the cassette. The first cycle is generated (1A4DH) followed by a 17 誑 delay and then the second cycle (1A4DH). Address ... 1A4DH

Address

@ (MSX only)

    This routine writes a single HI cycle with a length of approximately 396 誑 to the cassette. The length of each half of the cycle is taken from HIGH and control drops into the general cycle generator. Address ... 1A50H

Address

@ (MSX only)

    This routine writes a single cycle to the cassette. The length of the cycle's first half is supplied in register L and its second half in register H. The first length is counted down and then the Cas Out bit set via the PPI Mode Port. The second length is counted down and the Cas Out bit reset. - 80 - 4. ROM BIOS

    On all MSX machines the Z80 runs at a clock frequency of 3.579545 MHz (280 ns) with one wait state during the M1 cycle. As this routine counts every 16T states each unit increment in the length count represents a period of 4.47 誑. There is also a fixed overhead of 20.7 誑 associated with the routine whatever the length count.

    Address ... 1A63H (from 00EDH)
    Name ...... TAPION (Tape Input On)
    Input ..... None
    Exit ...... Flag C if CTRL-STOP termination
    Modifies .. AF, BC, DE, HL, DI

    Standard routine to turn the cassette motor on, read the cassette until a header is found and then determine the baud rate. Successive cycles are read from the cassette and the length of each one measured (1B34H). When 1,111 cycles have been found with less than 35 誑 variation in their lengths a header has been located.

    The next 256 cycles are then read (1B34H) and averaged to determine the cassette HI cycle length. This figure is multiplied by 1.5 and placed in LOWLIM where it defines the minimum acceptable length of a 0 start bit. The HI cycle length is placed in WINWID and will be used to discriminate between LO and HI cycles.

    Address ... 1ABCH (from 00EDH)
    Name ...... TAPIN (Tape Input)
    Input ..... None
    Exit ...... A=Byte read, Flag C if CTRL-STOP or I/O error
    Modifies .. AF, BC, DE, L

    Standard routine to read a byte of data from the cassette. The cassette is first read continuously until a start bit is found. This is done by locating a negative transition, measuring the following cycle length (1B1FH) and comparing this to see if it is greater than LOWLIM.

    Each of the eight data bits is then read by counting the number of transitions within a fixed period of time (1B03H). If zero or one transitions are found it is a 0 bit, if two or three are found it is a 1 bit. If more than three transitions are found the routine terminates with Flag C as this is presumed to be a hardware error of some sort. After the value of each bit has been determined a further one or two transitions are read (1B23H) to retain synchronization. With an odd transition count one more will be read, with an even transition count two more. Address ... 1B03H

Address

@ (MSX only)

    This routine is used by the TAPIN standard routine to count the number of cassette transitions within a fixed period of time. The window duration is contained in WINWID and is approximately 1.5 times the length of a HI cycle as shown below:

     +-- window --+
     |            |

    -+       +-------+
     |       |       |  LO Cycle
     |       |       |
     +-------+       +-

    -+   +---+   +---+
     |   |   |   |   |  HI Cycles
     |   |   |   |   |
     +---+   +---+   +-

Figure 40: Cassette Window.

    The Cas Input bit is continuously sampled via PSG Register 14 and compared with the previous reading held in register E. Each time a change of state is found register C is incremented. The sampling rate is once every 17.3 誑 so the value in WINWID, which was determined by the TAPION standard routine with a count rate of 11.45 誑, is effectively multiplied one and a half times. Address ... 1B1FH

Address

@ (MSX only)

    This routine measures the time to the next cassette input transition. The Cassette Input bit is continuously sampled via PSG Register 14 until it changes from the state supplied in register E. The state flag is then inverted and the duration count returned in register C, each unit increment represents a period of 11.45 誑. Address ... 1B34H

Address

@ (MSX only)

    This routine measures the length of a complete cassette cycle from negative transition to negative transition. The Cassette Input bit is sampled via PSG Register 14 until it goes to zero. The transition flag in register E is set to zero and the time to the positive transition measured (1B23H). The time to the negative transition is then measured (1B25H) and the total returned in register C.

    Address ... 1B45H (from 0018H)
    Name ...... OUTDO (Output to Default Output device)
    Input ..... A=Character to output
    Exit ...... None
    Modifies .. EI

    Standard routine used by the BASIC Interpreter to output a character to the current device. The ISFLIO standard routine is first used to check whether output is currently directed to an I/O buffer, if so control transfers to the sequential output driver (6C48H) via the CALBAS standard routine. If PRTFLG is zero control transfers to the CHPUT standard routine to output the character to the screen. Assuming the printer is active RAWPRT is checked. If this is non-zero the character is passed directly to the printer (1BABH), otherwise control drops into the OUTDLP standard routine.

    Address ... 1B63H (014DH)
    Name ...... OUTDLP (Output to Default Line Printer)
    Input ..... A=Character to output
    Exit ...... None
    Modifies .. EI

    Standard routine to output a character to the printer. If the character is a TAB code (09H) spaces are issued to the OUTDLP standard routine until LPTPOS is a multiple of eight (0, 8, 16 etc.) If the character is a CR code (0DH) LPTPOS is zeroed if it is any other control code LPTPOS is unaffected, if it is a displayable character LPTPOS is incremented.

    If NTMSXP is zero, meaning an MSX-specific printer is connected, the character is passed directly to the printer (1BABH). Assuming a normal printer is connected the CNVCHR standard routine is used to check for graphic characters. If the character is a header code (01H) the routine terminates with no action. If it is a converted graphic character it is replaced by a space, all other characters are passed to the printer (1BACH). Address ... 1B97H

Address

@ (MSX only)

    This twenty byte table is used by the keyboard decoder to find the correct routine for a given key number:

        KEY NUMBER  TO     FUNCTION
        ---------------------------------------
        00H to 2FH  0F83H  Rows 0 to 5
        30H to 32H  0F10H  SHIFT, CTRL, GRAPH
        33H         0F36H  CAP
        34H         0F10H  CODE
        35H to 39H  0FC3H  F1 to F5
        3AH to 3BH  0F10H  ESC, TAB
        3CH         0F46H  STOP
        3DH to 40H  0F10H  BS, CR, SEL, SPACE
        41H         0F06H  HOME
        42H to 57H  0F10H  INS, DEL, CURSOR

Address

@ (MSX only)

    This routine is used by the OUTDLP standard routine to pass a character to the printer. It is sent via the LPTOUT standard routine, if this returns Flag C control transfers to the "Device I/O error" generator (73B2H) via the CALBAS standard routine. Address ... 1BBFH

Address

@ (MSX only)

    The following 2 KB contains the power-up character set. The first eight bytes contain the pattern for character code 00H, the second eight bytes the pattern for character code 01H and so on to character code FFH.

    Address ... 23BFH (from 00AEH)
    Name ...... PINLIN (Prompt Input Line)
    Input ..... None
    Exit ...... HL=Start of text, Flag C if CTRL-STOP termination
    Modifies .. AF, BC, DE, HL, EI

    Standard routine used by the BASIC Interpreter Mainloop to collect a logical line of text from the console. Control transfers to the INLIN standard routine just after the point where the previous line has been cut (23E0H).

    Address ... 23CCH (from 00B4H)
    Name ...... QINLIN (Question Mark Input Line)
    Input ..... None
    Exit ...... HL=Start of text, Flag C if CTRL-STOP termination
    Modifies .. AF, BC, DE, HL, EI

    Standard routine used by the "INPUT" statement handler to collect a logical line of text from the console. The characters "? " are displayed via the OUTDO standard routine and control drops into the INLIN standard routine.

    Address ... 23D5H (from 00B1H)
    Name ...... INLIN (Input Line)
    Input ..... None
    Exit ...... HL=Start of text, Flag C if CTRL-STOP termination
    Modifies .. AF, BC, DE, HL, EI

    Standard routine used by the "LINE INPUT" statement handler to collect a logical line of text from the console. Characters are read from the keyboard until either the CR or CTRL-STOP keys are pressed. The logical line is then read from the screen character by character and placed in the Workspace Area text buffer BUF.

    The current screen coordinates are first taken from CSRX and CSRY and placed in FSTPOS. The screen row immediately above the current one then has its entry in LINTTB made non-zero (0C29H) to stop it extending logically into the current row.

    Each keyboard character read via the CHGET standard routine is checked (0919H) against the editing key table at 2439H. Control then transfers to one of the editing routines or to the default key handler (23FFH) as appropriate. This process continues until Flag C is returned by the CTRL-STOP or CR routines. Register pair HL is then set to point to the start of BUF and the routine terminates. Note that the carry, flag is cleared when Flag NZ is also returned to distinguish between a CR or protected CTRL-STOP termination and a normal CTRL-STOP termination. Address ... 23FFH

Address

@ (MSX only)

    This routine processes all characters for the INLIN standard routine except the special editing keys. If the character is a TAB code (09H) spaces are issued (23FFH) until CSRX is a multiple of eight plus one (columns 1, 9, 17, 25, 33). If the character is a graphic header code (01H) it is simply echoed to the OUTDO standard routine. All other control codes smaller than 20H are echoed to the OUTDO standard routine after which INSFLG and CSTYLE are zeroed. For the displayable characters INSFLG is first checked and a space inserted (24F2H) if applicable before the character is echoed to the OUTDO standard routine. Address ... 2439H

Address

@ (MSX only)

    This table contains the special editing keys recognized by the INLIN standard routine together with the relevant addresses:

        CODE TO    FUNCTION
        --------------------------------------------
        08H  2561H BS, backspace
        12H  24E5H INS, toggle insert mode
        1BH  23FEH ESC, no action
        02H  260EH CTRL-B, previous word
        06H  25F8H CTRL-F, next word
        0EH  25D7H CTRL-N, end of logical line
        05H  25B9H CTRL-E, clear to end of line
        03H  24C5H CTRL-STOP, terminate
        0DH  245AH CR, terminate
        15H  25AEH CTRL-U, clear line
        7FH  2550H DEL, delete character

Address

@ (MSX only)

    This routine performs the CR operation for the INLIN standard routine. The starting coordinates of the logical line are found (266CH) and the cursor removed from the screen (0A2EH). Up to 254 characters are then read from the VDP VRAM (0BD8H) and placed in BUF. Any null codes (00H) are ignored, any characters smaller than 20H are replaced by a graphic header code (01H) and the character itself with 40H added. As the end of each physical row is reached LINTTB is checked (0C1DH) to see whether the logical line extends to the next physical row. Trailing spaces are then stripped from BUF and a zero byte added as an end of text marker. The cursor is restored to the screen (09E1H) and its coordinates set to the last physical row of the logical line via the POSIT standard routine. A LF code is issued to the OUTDO standard routine, INSFLG is zeroed and the routine terminates with a CR code (0DH) in register A and Flag NZ and C. This CR code will be echoed to the screen by the INLIN standard routine mainloop just before it terminates. Address ... 24C5H

Address

@ (MSX only)

    This routine performs the CTRL-STOP operation for the INLIN standard routine. The last physical row of the logical line is found by examining LINTTB (0C1DH), CSTYLE is zeroed, a zero byte is placed at the start of BUF and all music variables are cleared via the GICINI standard routine. TRPTBL is then examined (0454H) to see if an "ON STOP" statement is active, if so the cursor is reset (24AFH) and the routine terminates with Flag NZ,C. BASROM is then checked to see whether a protected ROM is running, if so the cursor is reset (24AFH) and the routine terminates with Flag NZ,C. Otherwise the cursor is reset (24B2H) and the routine terminates with Flag Z and C. Address ... 24E5H

Address

@ (MSX only)

    This routine performs the INS operation for the INLIN standard routine. The current state of INSFLG is inverted and control terminates via the CSTYLE setting routine (242CH). Address ... 24F2H

Address

@ (MSX only)

    This routine inserts a space character for the default key section of the INLIN standard routine. The cursor is removed (0A2EH) and the current cursor coordinates taken from CSRX and CSRY. The character at this position is read from the VDP VRAM (0BD8H) and replaced with a space (0BE6H). Successive characters are then copied one column position to the right until the end of the physical row is reached.

    At this point LINTTB is examined (0C1DH) to determine whether the logical line is extended, if so the process continues on the next physical row. Otherwise the character taken from the last column position is examined, if this is a space the routine terminates by replacing the cursor (09E1H). Otherwise the physical row's entry in LINTTB is zeroed to indicate an extended logical line. The number of the next physical row is compared with the number of rows on the screen (0C32H). If the next row is the last one the screen is scrolled up (0A88H), otherwise a blank row is inserted (0AB7H) and the copying process continues. Address ... 2550H

Address

@ (MSX only)

    This routine performs the DEL operation for the INLIN standard routine. If the current cursor position is at the rightmost column and the logical line is not extended no action is taken other than to write a space to the VDP VRAM (2595H). Otherwise a RIGHT code (1CH) is issued to the OUTDO standard routine and control drops into the BS routine. Address ... 2561H

Address

@ (MSX only)

    This routine performs the BS operation for the INLIN standard routine. The cursor is first removed (0A2EH) and the cursor column coordinate decremented unless it is at the leftmost position and the previous row is not extended. Characters are then read from the VDP VRAM (0BD8H) and written back one position to the left (0BE6H) until the end of the logical line is reached. At this point a space is written to the VDP VRAM (0BE6H) and the cursor character is restored (09E1H). Address ... 25AEH

Address

@ (MSX only)

    This routine performs the CTRL-U operation for the INLIN standard routine. The cursor is removed (0A2EH) and the start of the logical line located (266CH) and placed in CSRX and CSRY. The entire logical line is then cleared (25BEH). Address ... 25B9H

Address

@ (MSX only)

    This routine performs the CTRL-E operation for the INLIN standard routine. The cursor is removed (0A2EH) and the remainder of the physical row cleared (0AEEH). This process is repeated for successive physical rows until the end of the logical line is found in LINTBB (0C1DH). The cursor is then restored (09E1H), INSFLG zeroed and CSTLYE reset to a block cursor (242DH). Address ... 25D7H

Address

@ (MSX only)

    This routine performs the CTRL-N operation for the INLIN standard routine. The cursor is removed (0A2EH) and the last physical row of the logical line found by examination of LINTTB (0C1DH). Starting at the rightmost column of this physical row characters are read from the VDP VRAM (0BD8H) until a non-space character is found. The cursor coordinates are then set one column to the right of this position (0A5BH) and the routine terminates by restoring the cursor (25CDH). Address ... 25F8H

Address

@ (MSX only)

    This routine performs the CTRL-F operation for the INLIN standard routine. The cursor is removed (0A2EH) and moved successively right (2624H) until a non-alphanumeric character is found. The cursor is then moved successively right (2624H) until an alphanumeric character is found. The routine terminates by restoring the cursor (25CDH). - 87 - 4. ROM BIOS Address ... 260EH

Address

@ (MSX only)

    This routine performs the CTRL-B operation for the INLIN standard routine. The cursor is removed (0A2EH) and moved successively left (2634H) until an alphanumeric character is found. The cursor is then moved successively left (2634H) until a non-alphanumeric character is found and then moved one position right (0A5BH). The routine terminates by restoring the cursor (25CDH). Address ... 2624H

Address

@ (MSX only)

    This routine moves the cursor one position right (0A5BH), loads register D with the rightmost column number, register E with the bottom row number and then tests for an alphanumeric character at the cursor position (263DH). Address ... 2634H

Address

@ (MSX only)

    This routine moves the cursor one position left (0A4CH), loads register D with the leftmost column number and register E with the top row number. The current cursor coordinates are compared with these values and the routine terminates Flag Z if the cursor is at this position. Otherwise the character at this position is read from the VDP VRAM (0BD8H) and checked to see if it is alphanumeric. If so the routine terminates Flag NZ and C otherwise it terminates Flag NZ and NC.

    The alphanumeric characters are the digits "0" to "9" and the letters "A" to "Z" and "a" to "z". Also included are the graphics characters 86H to 9FH and A6H to FFH, these were originally Japanese letters and should have been excluded during the conversion to the UK ROM. Address ... 266CH

Address

@ (MSX only)

    This routine finds the start of a logical line and returns its screen coordinates in register pair HL. Each physical row above the current one is checked via the LINTTB table (0C1DH) until a non-extended row is found. The row immediately below this on the screen is the start of the logical line and its row number is placed in register L. This is then compared with FSTPOS, which contains the row number when the INLIN standard routine was first entered, to see if the cursor is still on the same line. If so the column coordinate in register H is set to its initial position from FSTPOS. Otherwise register H is set to the leftmost position to return the whole line.

    Address ...2680H, JP to power-up initialize routine (7C76H).
    Address ...2683H, JP to the SYNCHR standard routine (558CH).
    Address ...2686H, JP to the CHRGTR standard routine (4666H).
    Address ...2689H, JP to the GETYPR standard routine (5597H).

    Address ... 015CH (MSX2, MSX2+, turbo R)
    Name ...... SUBROM (call Sub-ROM routine)
    Input ..... IX=Sub-Routine Address
    Exit ...... None (depends on the called sub-routine)
    Modifies .. IX, SP, AF' (others depend on the sub-routine)

    This routine calls a sub-routine in the extended sub-ROM. It calls the EXTROM BIOS standard routine and, before ending, pops the value on the top of the stack into IX, what means it won't return to the calling routine, but to the routine before it.

    Address ... 015FH (MSX2, MSX2+, turbo R)
    Name ...... EXTROM (call Extended ROM routine)
    Input ..... IX=Sub-Routine Address
    Exit ...... None (depends on the called sub-routine)
    Modifies .. AF' (others depend on the called sub-routine)

    This routine calls a sub-routine in the extended sub-ROM. It takes the slot ID from EXBRSA and calls CALSLT routine.

    Address ... 0168H (MSX2, MSX2+, turbo R)
    Name ...... EOL (delete till End-Of-Line)
    Input ..... H=X coordinate, L=Y coordinate
    Exit ...... None
    Modifies .. All registers

    This routine simply clears a text mode line from (H,L) until the end of the line. Upper left corner is (1,1).

    Address ... 016BH (MSX2, MSX2+, turbo R)
    Name ...... BIGFIL (Big Fill VRAM)
    Input ..... A=Data byte, BC=Length, HL=VRAM address
    Exit ...... None
    Modifies .. AF, BC, EI

    This routine does the same as FILVRM, but allows the access to all MSX2, MSX2+ and turbo R VRAM. It is also faster, because does not have VDP access delays.

    Address ... 016EH (MSX2, MSX2+, turbo R)
    Name ...... NSETRD (New Set VDP for Reading)
    Input ..... HL=VRAM address
    Exit ...... None
    Modifies .. AF, EI

    This routine does the same as SETRD, but allows access to all MSX2, MSX2+ and turbo R VRAM.

    Address ... 0171H (MSX2, MSX2+, turbo R)
    Name ...... NSTWRT (New Set VDP for Writing)
    Input ..... HL=VRAM address
    Exit ...... None
    Modifies .. AF, EI

    This routine does the same as SETWRT, but allows access to all MSX2, MSX2+ and turbo R VRAM.

    Address ... 0174H (MSX2, MSX2+, turbo R)
    Name ...... NRDVRM (New Read from VRAM)
    Input ..... HL=VRAM address
    Exit ...... None
    Modifies .. AF, EI

    This routine does the same as RDVRM, but allows access to all MSX2, MSX2+ and turbo R VRAM.

    Address ... 0177H (MSX2, MSX2+, turbo R)
    Name ...... NWRVRM (New Write to VRAM)
    Input ..... HL=VRAM address
    Exit ...... None
    Modifies .. EI

    This routine does the same as WRTVRM, but allows access to all MSX2, MSX2+ and turbo R VRAM.

    Address ... 017AH (MSX2+, turbo R)
    Name ...... RDRES (Read from Reset Port)
    Input ..... None
    Exit ...... A=Hardware Reset Port state
    Modifies .. None

    This routine reads the Hardware Reset Port status.

    Address ... 017DH (MSX2+, turbo R)
    Name ...... WRRES (Write to Reset Port)
    Input ..... A=Hardware Reset Port Datum
    Exit ...... None
    Modifies .. A

    This routine writes to the Hardware Reset Port.

    Address ... 0180H (turbo R)
    Name ...... CHGCPU (Change CPU mode)
    Input ..... A=CPU Mode
    Exit ...... None
    Modifies .. AF

    This routine changes the CPU mode and state LED according to the following configuration of the accumulator:

      7   6   5   4   3   2   1   0
    +---+---+---+---+---+---+-------+
    |LED| 0 | 0 | 0 | 0 | 0 | Mode  |
    +---+---+---+---+---+---+-------+

    Mode may be:

        00 = Z80
        01 = R800 ROM
        10 = R800 DRAM

    In ROM mode, BIOS and BASIC interpreter are used directly from system ROM, but in DRAM mode, they are copied to RAM and used from there. In turbo R, DRAM access is faster than ROM access, so in DRAM mode programs that access BIOS will run faster.

    If LED bit is 1, Mode LED will be turned on if R800 is activated or off if Z80 is activated. If LED is 0, the Mode LED will keep its current state (off in Z80 mode and on in R800 mode).

    Address ... 0183H (turbo R)
    Name ...... GETCPU (Get CPU mode)
    Input ..... None
    Exit ...... A=0 if Z80, A=1 if R800 ROM mode, A=2 if R800 DRAM mode
    Modifies .. F

    This routine reads the current CPU and BIOS mode as explained for the CHGCPU routine.

    Address ... 0186H (turbo R)
    Name ...... PCMPLY (PCM Play)
    Input ..... A=Mode, EHL=Data Address, DBC=Data Length
    Exit ...... C Flag=Termination State, A=Error Status, EHL=Error Pointer
    Modifies .. All registers

    This routine reads a sample of DBC bytes from the data buffer pointed by EHL and plays it with turbo R PCM. The accumulator defines the behaviour of the routine:

      7   6   5   4   3   2   1   0
    +---+---+---+---+---+---+-------+
    |Src| 0 | 0 | 0 | 0 | 0 | Freq. |
    +---+---+---+---+---+---+-------+

    The Frequency bits may have the following values:

        00 = 15.7500 KHz
        01 =  7.8750 KHz
        10 =  5.2500 KHz
        11 =  3.9375 KHz

    If Source Mode is 0, data are taken from the Main RAM, else if it is 1, data are taken from the VRAM.

    On exit, the routine returns 0 in the Carry Flag if the sample was taken without interruption. If it is set to 1, an abnormal termination occurred and the accumulator will have the following meaning:

        1 = Bad Frequency Appointment
        2 = Stop Key Interruption

    The Bad Frequency Appointment occurs if it tries to play a sample at a rate not supported by the current CPU mode. 15 KHz of sampling rate requires R800 DRAM mode.

    The EHL group of registers will point to the address where the error occurred.

    Address ... 0189H (turbo R)
    Name ...... PCMREC (PCM Record)
    Input ..... A=Mode, EHL=Data Address, DBC=Data Length
    Exit ...... C Flag=Termination State, A=Error Status, EHL=Error Pointer
    Modifies .. All registers

    This routine records a sample of size given by DBC from the turbo R PCM into a data buffer pointed by EHL. The accumulator defines the behaviour of the routine:

      7   6   5   4   3   2   1   0
    +---+---------------+---+-------+
    |Src| Trigger Level |Cpk| Freq. |
    +---+---------------+---+-------+

    The Src (Source Mode) and Freq. (Frequency) bits have the same meaning as for PCMPLY. The exit parameters are also the same.

    The Cpk bit defines if the sample is to be compressed (1) or not (0).

    The Trigger Level defines the sensibility of the PCM. If they are defined to a value of zero, for example, it will start immediately the recording.

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