Interrupt Controller (8259A)
D7
D6
D5
D4
D3
D2
D1
D0
0
0
0
1
LTIM
0
S
1
ICW1
D7
D6
D5
D4
D3
D2
D1
D0
S7
S6
S5
S4
S3
S2
S1
S0
D7
D6
D5
D4
D3
D2
D1
D0
A15
A14
A13
A12
A11
0
0
0
ICW2
ICW3 (Master Device)
NOTE 1: SLAVE ID IS EQUAL TO THE CORRESPONDING MASTER IR INPUT.
NOTE 2: X INDICATES "DON'T CARE."
D7
D6
D5
D4
D3
D2
D1
D0
0
0
0
FNM
1
AEOI
ICW4
0
0
0
0
0
ID2
ID1
ID0
D7
D6
D5
D4
D3
D2
D1
D0
ICW3 (Slave Device)
1 - SINGLE
0 - NOT SINGLE
1 - LEVEL TRIGGERED INPUT
0 - EDGE TRIGGERED INPUT
I/O ADDRESS = 20h
1 - IR INPUT HAS A SLAVE
0 - IR INPUT DOES NOT HAVE A
SLAVE
SET BY 8259A
ACCORDING TO INTERRUPT
LEVEL
MOST SIGNIFICANT
BITS OF VECTORING BYTE
I/O ADDRESS = 21h
I/O ADDRESS = 21h
1 - AUTO EOI
0 - NORMAL EOI
1 - FULLY NESTED MODE
0 - NOT FULLY NESTED MODE
I/O ADDRESS = 21h
SLAVE ID(1)
I/O ADDRESS = 21h
0
3
4
5
6
7
1
2
0
1
0
1
0
1
1
0
0
1
0
0
1
1
0
1
0
0
1
1
1
1
0
0
1
1
Figure 12–3. 8259A ICW Formats.
12-13