Figure C-1. Control Word Formats For The 82C55A - National Instruments PC-DIO-24/PnP User Manual

Appendix C Register-Level Programming
Control Word
Flag
1 = mode set
Mode Selection
00 = mode 0
01 = mode 1
1X = mode 2
Port A
1 = input
0 = output
Port C
(high nibble)
1 = input
0 = output
Control Word
Flag
0 = bit set/reset
Unused
Caution:
!
PC-DIO-24/PnP User Manual
Group A
D7 D6 D5
D6 D5
D7
b. Bit Set/Reset Word Format

Figure C-1. Control Word Formats for the 82C55A

During programming, note that each time any port is configured, output
ports A and C are reset to 0, and output port B is undefined.
Group B
D4 D3 D2
a. Mode Set Word Format
D3 D2
D4
C-4
D1 D0
Port C
(low nibble)
1 = input
0 = output
Port B
1 = input
0 = output
Mode Selection
0 = mode 0
1 = mode 1
D1 D0
Bit Set/Reset
1 = set
0 = reset
Bit Select
(000)
(001)
(010)
:
:
(111)
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