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Appendix C
Register-Level Programming
Group A
D7
D6
D5
Group B
D4
D3
D2
D1
D0
Control Word
Flag
1 = mode set
Port C
(low nibble)
1 = input
0 = output
Mode Selection
00 = mode 0
01 = mode 1
1X = mode 2
Port B
1 = input
0 = output
Mode Selection
0 = mode 0
1 = mode 1
Port A
1 = input
0 = output
Port C
(high nibble)
1 = input
0 = output
a. Mode Set Word Format
D7
D6
D5
D3
D4
D2
D1
Control Word
Flag
0 = bit set/reset
D0
Bit Set/Reset
1 = set
0 = reset
Bit Select
(000)
(001)
(010)
:
:
(111)
Unused
b. Bit Set/Reset Word Format
Figure C-1. Control Word Formats for the 82C55A
!
Caution:
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.
PC-DIO-24/PnP User Manual
C-4
© National Instruments Corporation