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D7
D6
OBFA*
INTEA
Bit
7
6
5–4
3
2
1
0
© National Instruments Corporation
Port C status-word bit definitions for output (port A and port B):
D5
D4
I/O
I/O
Name
Description
OBFA*
Output Buffer for Port A—A low setting indicates that
the CPU has written data to port A.
INTEA
Interrupt Enable Bit for Port A—Setting this bit
enables interrupts from port A of the 82C55A. This bit
is controlled by setting/resetting PC6.
I/O
Input/Output—These bits can be used for general-
purpose I/O when port A is in mode 1 output. If these
bits are configured for output, the port C bit set/reset
function must be used to manipulate them.
INTRA
Interrupt Request Status for Port A—When INTEA
and OBFA* are high, this bit is high, indicating that an
interrupt request is pending for port A.
INTEB
Interrupt Enable Bit for Port B—Setting this bit
enables interrupts from port B of the 82C55A. This bit
is controlled by setting/resetting PC2.
OBFB*
Output Buffer for Port B—A low setting indicates that
the CPU has written data to port B.
INTRB
Interrupt Request Status for Port B—When INTEB
and OBFB* are high, this bit is high, indicating that an
interrupt request is pending for port B.
At the digital I/O connector, port C has the following pin assignments
when in mode 1 output. Notice that the status of ACKA* and the status
of ACKB* are not included when port C is read.
Appendix C
D3
D2
INTRA
INTEB
C-15
Register-Level Programming
D1
D0
OBFB*
INTRB
PC-DIO-24/PnP User Manual
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