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Register-Level Programming Chapter 4
Lab-NB User Manual 4-62 © National Instruments Corporation
Port C status-word bit definitions for output (port A and port B):
76543210
OBFA* INTEA I/O I/O INTRA INTEB* OBFB INTRB
Bit Name Description
7 OBFA* Output Buffer Full for Port A—Low indicates that the CPU has
written data out to port A.
6 INTEA Interrupt Enable Bit for Port A—If this bit is high, interrupts are
enabled from the 82C55A for port A. Controlled by setting or
resetting PC6.
5, 4 I/O Input/Output—Extra I/O status line when port A is in mode 1
output.
3 INTRA Interrupt Request Status for Port A—When INTEA is high and
OBFA* is high, this bit is high, indicating that an interrupt request
is asserted.
2 INTEB Interrupt Enable Bit for Port B—If this bit is high, interrupts are
enabled from the 82C55A for port B. Controlled by setting or
resetting PC2.
1 OBFB* Output Buffer Full for Port B—Low indicates that the CPU has
written data out to port B.
0 INTRB Interrupt Request Status for Port B—When INTEB is high and
OBFB* is high, this bit is high, indicating that an interrupt request
is asserted.
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 ACKB* is not provided when port C is read.
OBFA*PC7
PC6
PC5
PC4
PC3
PC2
PC1
PC0
I/O
INTRA
ACKB*
OBFB*
INTRB
I/OGroup A
Group B
ACKA*