E-7
D
ed
ic
a
te
d
&
U
se
r
I/
O
P
C
I
PCI
The following table shows the configuration of the 24 User I/O lines for the PCI.
Figure E-8
User I/O Availabel on the PCI
Both Dedicated and User I/O signals originate from 82C55 programmable I/O controllers.
These signals can be programmed in groups of 8 as inputs or outputs.
Bit
Description Pin
Bit
Description Pin
Bit Description
Pin
0
User Port A
(8-bits input
or output)
1
8
User Port B
(8-bits input
or output)
9
16
User Port C
(8-bits input
or output)
17
1
2
9
10
17
18
2
3
10
11
18
19
3
4
11
12
19
20
4
5
12
13
20
21
5
6
13
14
21
22
6
7
14
15
22
23
7
8
15
16
23
24
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