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D-29
SYSTEM REGISTER QUICK REFERENCE
D.24 ICW2 (MASTER AND SLAVE)
D.25 ICW3 (MASTER)
Initialization Command Word 2
ICW2 (master and slave)
(write only)
Expanded Addr:
ISA Addr:
Reset State:
master slave
F021H F0A1H
0021H 00A1H
XXH XXH
7 0
T7 T6 T5 T4 T3 0 0 0
Bit
Number
Bit
Mnemonic
Function
7–3 T7:3 Base Interrupt Type:
Write the base interrupt vector’s five most-significant bits to these bits.
2–0 T2:0 Clear these bits to guarantee device operation.
Initialization Command Word 3
ICW3 (master)
(write only)
Expanded Addr:
ISA Addr:
Reset State:
F021H
0021H
XXH
7 0
S7 S6 S5 S4 S3 S2 S1 0
Bit
Number
Bit
Mnemonic
Function
7–3 S7:3 Slave IRs
0 = No slave 8259A is attached to the corresponding IR signal of the
master.
1 = A slave 82C59A is attached to the corresponding IR signal of the
master.
2 S2 0 = Internal slave not used
1 = Internal slave is cascaded from the master’s IR2 signal.
1 S1 Slave IRs
0 = No slave 8259A is attached to the master through the IR1 signal of
the master.
1 = A slave 82C59A is attached to the IR1 signal of the master.
0 — Clear this bit to guarantee device operation.