ACT apricot - Operational Command Words

INTERRUPT CONTROLLER
assigns the following interrupt numbers to the interrupt
request lines.
IR
Input Type Vector
0
lOP SINTRl SOH
1 lOP SINTR2 5lH
2
INT2 52H
3
INT3 53H
4
FDC INT 54H
5
SIO INT
55H
6
TMROUTO 56H
7
NDP INT
57H
The majority of the features provided by ICW4 are for use
with systems utilising more than one PIC and therefore not
relevant to the single PIC environment operated on the
System Board. The command word still has to be issued, to
provide the PIC with the following information:
(a) The associated CPU is an 8086 device.
(b) Termination of an interrupt service routine is to be
signified by software
using an Operational Control
Word, and not by the automatic end of interrupt
facility (AEOI), available during the hardware interrupt
acknowledge cycle. (AEOI is only suitable for systems
with interrupts which occur at a predetermined rate).
The required format for ICW 4 is as detailed below and is
written to the address location 02H in the system input/
output space.
I 0 I 0 I 0 I 0 I 0 I x I 0 I 1 I ICW4
Operational Command Words
After initialization the interrupt request lines are all
operative
with a decreasing order of priority from IRO
through to IR7 (i.e. IRO highest priority, IR7Iowest). The
operation of the PIC can then be further controlled or