Chapter 4
Programming
© National Instruments Corporation
4-85
AT-MIO-16D User Manual
Port C bits PC4 and PC5
1 = input
0 = output
1
0
X
X
X
0
1/0
1
7
6
5
4
3
2
1
0
The control word written to the DIO-24 CNFG Register to configure Port B for output in Mode 1
is shown as follows. Notice that Port B does not have extra input or output lines from Port C.
1
X
0
X
X
X
1
X
7
6
5
4
3
2
1
0
During a Mode 1 data write transfer, the status of the handshaking lines and interrupt signals can
be obtained by reading Port C. Notice that the bit definitions are different for a write and a read
transfer.
The following are the 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 to Port A.
6
INTEA
Interrupt enable bit for Port A. If this bit is high, DIO interrupts
are enabled from the 82C55A 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 a DIO interrupt
request is asserted.
2
INTEB
Interrupt enable bit for Port B. If this bit is high, interrupts are
enabled from the 82C55A 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 a DIO interrupt
request is asserted.
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