Initialization Command Word 2 (Icw2); Initialization Command Word 2 Register (Icw2) - Intel 386 User Manual

9.3.4

Initialization Command Word 2 (ICW2)

Use the ICW2 register to define the base interrupt vector for the 82C59A. Valid vector numbers
for maskable interrupts range from 32 to 255. Because the base vector number must reside on an
8-byte boundary, the valid base vector numbers are 32 + n × 8 where 0
interrupt vector's five most-significant bits to ICW2's five most-significant bits. The 82C59A de-
termines specific IR signal vector numbers by adding the number of the IR signal to the base in-
terrupt vector.
Initialization Command Word 2
ICW2 (master and slave)
(write only)
7
T7 T6
Bit Bit
Number Mnemonic
7–3 T7:3
2–0 T2:0
Figure 9-9. Initialization Command Word 2 Register (ICW2)
T5 T4
Base Interrupt Type:
Write the base interrupt vector's five most-significant bits to these bits.
Clear these bits to guarantee device operation.
INTERRUPT CONTROL UNIT
n
master
Expanded Addr: F021H
ISA Addr: 0021H
Reset State: XXH
T3 0
Function
27. Write the base
slave
F0A1H
00A1H
XXH
0
0 0
9-21