Appendix B
Register-Level Programming — Register Map and Description
©
National Instruments Corporation
B-7
PCI-DIO-96/PXI-6508/PCI-6503 User Manual
Figure B-2.
Control Word Formats for the 82C55A
D7
D6
D5
D4
D3
D2
D1
D0
Group A
Group B
Mode Selection
00 = Mode 0
01 = Mode 1
1X = Mode 2
Control Word Flag
1 = Mode Set
Port A
1 = Input
0 = Output
Port C
(high nibble)
1 = Input
0 = Output
Port C
(low nibble)
1 = Input
0 = Output
Port B
1 = Input
0 = Output
Mode Selection
0 = Mode 0
1 = Mode 1
a. Control Word Flag, Mode Set (bit 7 = 1)
D7
D6
D5
D4
D3
D2
D1
D0
Control Word Flag
0 = Bit Set/Reset
Unused
Bit Set/Reset
1 = Set
0 = Reset
Bit Select
(000)
(001)
(010)
:
:
(111)
b. Control Word Flag, Bit Set/Reset (bit 7 = 0)