Mode 1-Strobed Output - National Instruments PC-DIO-96 User Manual

Chapter 4
Mode 1—Strobed Output
The control word written to the CNFG Register to configure port A for output in mode 1 is
shown as follows. Bits PC4 and PC5 of port C can be used as extra input or output lines.
The control word written to the 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.
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.
Port C status-word bit definitions for output (port A and port B):
D7 D6
OBFA* INTEA
Bit Name
7 OBFA*
6 INTEA
5–4 I/O
3 INTRA
© National Instruments Corporation
D7 D6 D5
D4
1 0
1 0
D7 D6 D5
D4
1
X X
X
D5 D4
I/O I/O
Description
Output Buffer for Port A—A low setting indicates that the CPU
has written data to port A.
Interrupt Enable Bit for Port A—Setting this bit enables interrupts
from port A of the 82C55A. This bit is controlled by
setting/resetting PC6.
Input/Output—These bits can be used for general-purpose I/O
when port A is in mode 1 output. If these bits are configured for
output, the port C bit set/reset function must be used to manipulate
them.
Interrupt Request Status for Port A—When INTEA and OBFA*
are high, this bit is high, indicating that an interrupt request is
pending for port A.
D3 D2 D1 D0
X
1/0 X X
Port C bits PC4 and PC5
1 = input
0 = output
D3 D2 D1 D0
1 0 X
X
D3 D2
INTRA INTEB
4-15
Register-Level Programming
D1 D0
OBFB* INTRB
PC-DIO-96 User Manual