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Servicing Personal Computers, 3rd Edition
book

Servicing Personal Computers, 3rd Edition

by Michael Tooley
May 2014
Intermediate to advanced content levelIntermediate to advanced
320 pages
13h 41m
English
Newnes
Content preview from Servicing Personal Computers, 3rd Edition
Servicing the IBM
PC
and compatibles 241
5. Upon receiving the INTA pulse from the processor, the highest priority ISR bit is set and the
corresponding IRR bit is reset.
6. The processor then initiates a second interrupt acknowledge (INTA) pulse. During this
second period for which the INTA line is taken low, the 8259 outputs a pointer on the data
bus to be read by the processor.
The internal architecture and pin connections for the 8259A are shown in Figures 6.24 and
6.25 respectively.
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7
D
6
D
5
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4
D
3
D
2
D
1
D
0
C
C
C
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c
c
c
c
c
c
CASO
C
CAS
1
GND
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c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
^^r
28
27
26
25
24
23
22
8259A21
20
19
18
17
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Publisher Resources

ISBN: 9781483193670