Appendix C
Register-Level Programming
PC-DIO-24/PnP User Manual
C-12
©
National Instruments Corporation
The control word written to the CNFG Register to configure port B for
input in mode 1 is shown as follows. Notice that port B does not have
extra input or output lines left from port C when ports A and B are both
enabled for handshaking.
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.
Port C status-word bit definitions for input (port A and port B):
Bit
Name
Description
7–6
I/O
Input/Output—These bits can be used for general-
purpose I/O when port A is in mode 1 input. If these
bits are configured for output, the port C bit set/reset
function must be used to manipulate them.
5
IBFA
Input Buffer for Port A—A high setting indicates that
data has been loaded into the input latch for port A.
4
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 PC4.
3
INTRA
Interrupt Request Status for Port A—When INTEA
and IBFA are high, this bit is high, indicating that an
interrupt request is pending for port A.
2
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.
1
IBFB
Input Buffer for Port B—A high setting indicates that
data has been loaded into the input latch for port B.
D7
D6
D5
D4
D3
D2
D1
D0
I/O
I/O
IBFA
INTEA
INTRA
INTEB
IBFB
INTRB
D2
D1
D0
D3
D7
D6
D5
D4
1
X
X
X
1
1
X
X
