User manual

Appendix D Register-Level Programming

National Instruments Corporation D-15 PC-DIO-96/PnP User Manual

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 from port C.

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.

D7 D6 D5 D4 D3 D2 D1 D0

I/O I/O IBFA INTEA INTRA INTEB IBFB INTRB

D2 D1 D0D3D7

D6 D5

1 = input

0 = output

Port C bits PC6 and PC7

1/0

X11

D2 D1 D0D3D7

D6 D5

X11X