National Instruments Low-Cost Multifunction I/O Board for ISA Lab-PC+ User Manual
Page 186
Register-Level Programming
Appendix E
Lab-PC+ User Manual
E-30
© National Instruments Corporation
Port C status-word bit definitions for output (Port A and Port B):
7
6
5
4
3
2
1
0
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 8255A for Port A. Controlled by bit set/reset of
PC6.
5,4
I/O
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 8255A for Port B. Controlled by bit set/reset of
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/O
Group A
Group B
ACKA*