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Appendix C Register-Level Programming
©
National Instruments Corporation C-9 PC-DIO-24/PnP User Manual
Mode 2
Use this mode for communication over a bidirectional 8-bit bus.
Handshaking signals are used in a manner similar to mode 1. Mode 2 is
available for use in group A only (port A and the upper portion of
port C). Other features of this mode include the following:
• One 8-bit bidirectional port (port A) and a 5-bit control/status port
(port C).
• Latched inputs and outputs.
• Interrupt generation and enable/disable functions.
Single Bit Set/Reset Feature
You can set or reset any of the eight bits of port C with one control
word. This feature generates control signals for port A and port B when
these ports are operating in mode 1 or mode 2.
Mode 0—Basic I/O
Use mode 0 for simple I/O functions (no handshaking) for each of the
three ports. You can assign each port as an input or an output port. The
16 possible I/O configurations are shown in Table C-3. Notice that bit 7
of the control word is set when programming the mode of operation for
each port.
Table C-3.
Mode 0 I/O Configurations
Number
Control Word Group A Group B
Bit
76543210
Port A Port C
1
Port B Port C
2
0 10000000 Output Output Output Output
1 10000001 Output Output Output Input
2 10000010 Output Output Input Output
3 10000011 Output Output Input Input
4 10001000 Output Input Output Output
5 10001001 Output Input Output Input
6 10001010 Output Input Input Output
7 10001011 Output Input Input Input
8 10010000 Input Output Output Output