National Instruments PC-DIO-96/PnP, User Manual

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Appendix D Register-Level Programming
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National Instruments Corporation D-21 PC-DIO-96/PnP User Manual
Mode 2—Bidirectional Bus
Mode 2 has an 8-bit bus that can transfer both input and output data
without changing the configuration. The data transfers are synchronized
with handshaking lines in port C. This mode uses only port A; however,
port B can be used in either mode 0 or mode 1 while port A is configured
for mode 2.
The control word written to the CNFG Register to configure port A as
a bidirectional data bus in mode 2 is shown as follows. If port B is
configured for mode 0, then PC2, PC1, and PC0 of port C can be used
as extra input or output lines.
Figure D-5. Port A Configured as a Bidirectional Data Bus in Mode 2
During a mode 2 data transfer, the status of the handshaking lines and
interrupt signals can be obtained by reading port C. The port C status-
word bit definitions for a mode 2 transfer are shown as follows.
D2 D1 D0 D3 D7 D6 D5
D4
1 = input
0 = output
Port C
(PC2-PC0)
1
1/0 X X X 1
1 = input
0 = output
Port B
0 = mode 0
1 = mode 1
Group B Mode
1/0
1/0