May 2014
Intermediate to advanced
320 pages
13h 41m
English
Content preview from Servicing Personal Computers, 3rd Edition
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236
I
n-
Control
r
egi
st
er
L
4E
Figure
6.19.
Internal architecture
of
the
8253
D2
DO
::
E":
ia
CLKZ
Counter
-i
-CLK
2
-GATE
2
-OUT
2
GND
412 13pOUT1
Figure
6.20.
8253
pin connections
237
D
7
-°0
Rr-i t/PBy-PBo
Figure
6.21.
Internal architecture of the 8255A
PA3 d
PA2 d
PA1 □
PAO d
RD d
es
d
GND d
Al C
AO C
PC7 C
PC6 C
PC5 C
PC4 C
PCO C
PC1 C
PC2 C
PC3 C
PBO C
PB1 C
PB2 C
1
2
3
4
5
6
7
8
Θ
10
11
12
13
I
14
15
16
17
18
1
19
J20
w
40
39
38
37
36
35
34
33
32
31
3255A 30
29
28
27
26
25
24
23
22
21
D PA4
D PA5
Ώ
ΡΑ6
2 PA7
3 WR
3 RESET
3D
0
3D,
DD
2 ...