Specifications

Interrupt Controller (8259A)
M7 M6 M5 M4 M3 M2 M1 M0
INTERRUPT MASK
1 = MASK SET
0 = MASK RESET
D7 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1 D0
0 3456712
0 1010110
0 1001101
0 0111100
R SL EOI 0 0 L2 L1 L0
BCD LEVEL TO BE RESET
OR PUT INTO LOWEST PRIORITY
0
0
1
1
0
1
1
0
0
1
0
0
0
1
1
1
1
1
1
0
0
1
0
0
Non-specific EOI
Specific EOI
Rotate on Non-Specific EOI Command
Rotate in Automatic EOI Mode (Set)
Rotate in Automatic EOI Mode (Clear)
*Set Priority Command
No operation
*Rotate on Specific EOI Command
OCW2
D7 D6 D5 D4 D3 D2 D1 D0
ESMM
SMM 0 1 P RR RIS
0
0
1
0
0
1
1
1
NO ACTION
READ
IRR
ON NEXT
RD PULSE
READ
ISR
ON NEXT
RD PULSE
0
0
1
0
0
1
1
1
NO ACTION
RESET
SPECIAL
MASK
SET
SPECIAL
MASK
POLLING
A HIGH ENABLES THE NEXT RD PULSE
TO READ THE BCD CODE OF THE HIGH-
EST LEVEL REQUESTING INTERRUPT
OCW3
READ IN-SERVICE REGISTER
I/O ADDRESS = 20h
0
I/O ADDRESS = 20h
I/O ADDRESS = 21h
OCW1
Figure 12–4. 8259A Operation Control Word Formats.
12-17