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8259a Programmable Interrupt Controller


 
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I/O ports

offset read write
0x000 IRR, ISR, IntVec ICW1,OCW2,OCW3
0x001 IMR ICW2,ICW3,ICW4,OCW1

7 6 5 4 3 2 1 0
0Set this bit to 0 0Set this bit to 0 0Set this bit to 0 1Set this bit to 1 LVT0: Edge triggered, 1: Level triggered 0Set this bit to 0 IC30: Expect ICW1 and ICW2 only, 1: Expect ICW3 IC4Expect ICW4
PIC Initialisation command word 1

7 6 5 4 3 2 1 0
OFSM.S. 5 bits that make up the INT number, L.S. 3 bits come from IRQ level 0-7 0Set this bit to 0 0Set this bit to 0 0Set this bit to 0
PIC Initialisation command word 2

7 6 5 4 3 2 1 0
S70: IRQ line connected to device, 1: IRQ line connected to slave PIC S60: IRQ line connected to device, 1: IRQ line connected to slave PIC S50: IRQ line connected to device, 1: IRQ line connected to slave PIC S40: IRQ line connected to device, 1: IRQ line connected to slave PIC S30: IRQ line connected to device, 1: IRQ line connected to slave PIC S20: IRQ line connected to device, 1: IRQ line connected to slave PIC S10: IRQ line connected to device, 1: IRQ line connected to slave PIC S00: IRQ line connected to device, 1: IRQ line connected to slave PIC
PIC Initialisation command word 3 for a master PIC

7 6 5 4 3 2 1 0
0Set this bit to 0 0Set this bit to 0 0Set this bit to 0 0Set this bit to 0 0Set this bit to 0 IDUnique slave id
PIC Initialisation command word 3 for a slave PIC

7 6 5 4 3 2 1 0
0Set this bit to 0 0Set this bit to 0 0Set this bit to 0 NSTNested mode BUFBuffered mode MSTMaster AEIAutomatic EOI 1Set this bit to 1
PIC Initialisation command word 4

7 6 5 4 3 2 1 0
D7Disable IRQ 7 D6Disable IRQ 6 D5Disable IRQ 5 D4Disable IRQ 4 D3Disable IRQ 3 D2Disable IRQ 2 D1Disable IRQ 1 D0Disable IRQ 0
PIC Operation command word 1

7 6 5 4 3 2 1 0
OPROperation 0Set this bit to 0 0Set this bit to 0 LVLLevel. Only used in operations marked (L)
PIC Operation command word 2

OPERATION   000 Rotate AEOI
            001        EOI
            010 NOP
            011        EOI  (L)
            100 Rotate AEOI setMode
            101 SetPriority Instruction
            110 Rotate EOI
            111 Rotate EOI  (L)
	

7 6 5 4 3 2 1 0
0Set this bit to 0 OP1Operation 1 0Set this bit to 0 1Set this bit to 1 POLPoll instruction OP2Operation 2
PIC Operation command word 3

OP1 00  NOP
    01  NOP
    10  Cancel Mask
    11  Set Mask
OP2 00  NOP
    01  NOP
    10  Read IRR
    11  Read ISR
	
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This page was updated on
Sun 13 December 1998
http://www.thesky.demon.co.uk/pc-hardware/8259a.html