Mode 2-Bidirectional Bus - National Instruments PCI-DIO-96 User Manual

Appendix B Register-Level Programming — Port C Status-Word Bit Definitions for Output (Ports A and B)
Mode 2—Bidirectional Bus
Note For mode 2 examples, you must configure the don't care bits appropriately in the
control word if you want to use the other ports in combination with the example.
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.
Figure B-10 shows the control word written to the Configuration Register to configure port A
as a bidirectional data bus in mode 2. If port B is configured for mode 0, you can use PC2,
PC1, and PC0 of port C as extra input or output lines.
Figure B-10. Control Word to Configure Port A as Mode 2 Bidirectional Data Bus
During a mode 2 data transfer, you can obtain the status of the handshaking lines and interrupt
signals by reading port C. The following sections show the port C status-word bit definitions
for a mode 2 transfer.
PCI-DIO-96/PXI-6508/PCI-6503 User Manual
D7 D6 D5 D4
1 1 X X
D3 D2 D1 D0
X 1/0 1/0 1/0
B-26
Port C
PC <2..0>
1 = Input
0 = Output
Port B
1 = Input
0 = Output
Group B Mode
0 = Mode 0
1 = Mode 1
ni.com