National Instruments PC-DIO-96 用户手册

Port C status-word bit definitions for bidirectional data path (port A only):

D7

D6

D5

D4

D3

D2

D1

D0

OBFA*

INTE1

IBFA

INTE2

INTRA

I/O

I/O

I/O

7

OBFA*

Output Buffer for Port A—A low setting indicates that the CPU
has written data to port A.

6

INTE1

Interrupt Enable Bit for Port A Output Interrupts—Setting this bit
enables output interrupts from port A of the 82C55A.  This bit is
controlled by setting/resetting PC6.

5

IBFA

Input Buffer for Port A—A high setting indicates that data has
been loaded into the input latch of port A.

4

INTE2

Interrupt Enable Bit for Port A Input Interrupts—Setting this bit
enables input interrupts from port A of the 82C55A.  This bit is
controlled by setting/resetting PC4.

3

INTRA

Interrupt Request Status for Port A—If INTE1 and IBFA are high,
then this bit is high, indicating that an interrupt request is pending
for port A input transfers.  If INTE2 and OBFA* are high, then this
bit is high, indicating that an interrupt request is pending for port A
output transfers.

2–0

I/O

Input/Output—These bits can be used for general-purpose I/O lines
if group B is  configured for mode 0.  If group B is configured for
mode 1, refer to the bit explanations shown in the preceding mode
1 sections.

At the digital I/O connector, port C has the following pin assignments when in mode 2.  Notice
that the status of STBA* and the status of ACKA* are not included in the port C status word.

PC7

PC6

PC5

PC4

PC3

PC2

PC1

PC0

OBFA*

ACKA*

IBFA

STBA*

INTRA

#

#

#

Group A

Group B

#

The three port C lines associated with group B function based on the mode selected for group B;

that is, if group B is configured for mode 0, PC2-PC0 function as general-purpose I/O, but if group B is
configured for mode 1 input or output, PC2-PC0 function as handshaking lines as shown in the
preceding mode 1 sections.