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Register-Level Programming Chapter 4
Lab-NB User Manual 4-64 © National Instruments Corporation
Port C status-word bit definitions for bidirectional data path (port A only):
76543210
OBFA* INTE1 IBFA INTE2 INTRA I/O I/O I/O
Bit Name Description
7 OBFA* Output Buffer Full—Low indicates that the CPU has written data
out to port A.
6 INTE1 Interrupt Enable Bit for Output—If this bit is set, interrupts are
enabled from the 82C55A for OBF*. Controlled by setting or
resetting PC6.
5 IBFA Input Buffer Full—High indicates that data has been loaded into
the input latch of port A.
4 INTE2 Interrupt Enable Bit for Input—If this bit is set, interrupts are
enabled from the 82C55A for IBF. Controlled by setting or
resetting PC4.
3 INTRA Interrupt Request Status—If INTE1 is high and IBFA is high, this
bit is high, indicating that an interrupt request is asserted for input
transfers. If INTE2 is high and OBFA* is high, this bit is high,
indicating that an interrupt request is asserted for output transfers.
2–0 I/O Input/Output—Extra I/O status lines available if port B is not
configured for mode 1.
At the digital I/O connector, port C has the following pin assignments when in mode 2.
OBFA*PC7
PC6
PC5
PC4
PC3
PC2
PC1
PC0
STBA*
INTRA
IBFA
Group A
ACKA*
I/O
I/O
I/O