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Appendix B
Register-Level Programming
©
National Instruments Corporation
B-19
DAQCard-DIO-24 User Manual
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.
The following are port C status-word bit definitions for bidirectional
bus data path (port A only).
Bit
Name
Description
7
OBFA*
Output Buffer Full for Port A—Low
indicates that the CPU has written data to
port A.
6
INTE1
Interrupt Enable Bit for Output—If this
bit is set, interrupts are enabled from the
82C55A for OBFA*. Controlled by bit
set/reset of PC6.
5
IBFA
Input Buffer Full for Port A—High
indicates that data has been loaded into
the input latch for port A.
7
6
5
4
3
2
1
0
OBFA*
INTE1
IBFA
INTE2
INTRA
I/O or port B handshaking
1/0
1/0
1/0
X
X
X
1
1
Port C bits PC2, PC1, PC0
1 = input
0 = output
Port B direction
1 = input
0 = output
Group B mode
0 = mode 0
1 = mode 1
7
6
5
4
3
2
1
0