Macintosh IIfx VIA Registers
VIA Registers*
VIA1 Data Register A Bit
Direction Bit Name Description 6 Input
CPU.ID3 Bit 3 of 4 bit model identity code1 4 Input CPU.ID2 Bit 2 of 4 bit model identity code1 2
Input
CPU.ID1 Bit 1 of 4 bit model identity code1 1 Input CPU.ID0 Bit 0 of 4 bit model identity code1 VIA1 Data Register B
7 Output vSndEnb 0 = Sound Enable (for software compatability) 2 Output rTCEnb 0 = Real Time Clock enabled 1 Output rtcCLK RTC's data clock line 0 Input/Output rtcData RTC's serial data line 1- The CPUID the Macintosh IIfx has a value of 1101.
VIA2 Data Register A Bit
Direction
Bit Name
Description
7
Output
v2RAM1 RAM-size bit 1 6
Output
v2RAM0 RAM-size bit 0 5
Input
v2IRQ6 Interrupt request from expansion slot $E 4
Input
v2IRQ5 Interrupt request from expansion slot $D 3
Input
v2IRQ4 Interrupt request from expansion slot $C 2
Input
v2IRQ3 Interrupt request from expansion slot $B 1
Input
v2IRQ2 Interrupt request from expansion slot $A 0
Input
v2IRQ1 Interrupt request from expansion slot $9 VIA2 Data Register B
7 Output
v2VBL 60.15 Hz interrupt request to VIA1 7
Input
v2SNDEXT 0 = plug is inserted in external sound jack 5 Input
v2TM0A Transfer mode acknowledge bit 0 from NuBus 4
Input
v2TM1A Transfer mode acknowledge bit 1 from NuBus 2
Output
v2PowerOff 0 = shut power off 1 Output v2BusLk 0 = NuBus transactions are locke out 0 Output v2CDis 0 = disable instruction/data cache * Information gathered from Guide to Macintosh Family Hardware.