National Instruments PC-DIO-24 User Manual page 38

Register-Level Programming
During a mode 1 data read 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 an input transfer are
shown as follows.
The following are the port C status-word bit definitions for input (port A and port B).
7 6
I/O I/O
Bit Name
7–6 I/O
5 IBFA
4 INTEA
3 INTRA
2 INTEB
1 IBFB
0 INTRB
At the digital I/O connector, port C has the following pin assignments when in mode 1 input.
Notice that the status of STBA* and STBB* are not included in the port C status word.
PC-DIO-24 User Manual
5 4
IBFA INTEA
Description
Input/Output—Extra I/O status lines when port A is in mode 1
input.
Input Buffer Full for Port A—High indicates that data has been
loaded into the input latch for port A.
Interrupt Enable Bit for Port A—Enables interrupts from the
82C55A for port A. Controlled by bit set/reset of PC4.
Interrupt Request Status for Port A—When INTEA is high and
IBFA is high, this bit is high, indicating that an interrupt request is
asserted.
Interrupt Enable Bit for Port B—Enables interrupts from the
82C55A for port B. Controlled by bit set/reset of PC2.
Input Buffer Full for Port B—High indicates that data has been
loaded into the input latch for port B.
Interrupt Request Status for Port B—When INTEB is high and
IBFB is high, this bit is high, indicating that an interrupt request is
asserted.
Group A
Group B
3 2
INTRA INTEB
PC7 I/O
PC6 I/O
PC5 IBFA
PC4 STBA*
PC3 INTRA
PC2 STBB*
PC1 IBFB
PC0 INTRB
4-8 © National Instruments Corporation
Chapter 4
1 0
IBFB INTRB