Port Data Register - Keysight VXI Bus 75000 C Series User And Programming Manual

Register Descriptions
I/O. This is a read/write bit. Read this bit to find the current status of the I/O line,
which is an output line to the peripheral from the port data transceiver. If bit 6 is
equal to 0, the line is FALSE and the transceiver is enabled for output. If bit 6 is
equal to 1, the line is TRUE and the transceiver is enabled for input. This bit is
equal to 1 (input) after a hardware reset. You can select input or output by
changing this bit.
CTL. This is a read/write bit. Read this bit to find the current state of the CTL line.
A 1 shows the line is TRUE; a 0 shows the line is FALSE (the bit is not
normalized). When handshaking is enabled (bit 1 of the Port Transfer Control
Register is set), the CTL line is controlled by the port controller. To prevent
incorrect handshaking due to interaction with other lines, before enabling
handshaking set the control line to FALSE.
If handshaking is not enabled and the handshake mode is set to NONE, you can
control the logical state of the CTL line by writing a normalized 1 or 0 to bit 7.

Port Data Register

The Port Data Register is a read/write register. It is used for both output and
input. Its operation depends on the state of the I/O bit in the Port Status/Control
Register. The ports affected by this register are set by the BB1 and BB0 bits in
the Card Status/Control Register.
Keysight E1458A 96-Channel Digital I/O Module User Guide
If you are using the port handshake lines to control transfers, use
the I/O line to control the direction of data transfer to your
peripheral. Make sure that the peripheral is always enabled to send
data during input transfers and to receive data during output
transfers.
base+2C16, base+2D16, base+2E16, base+2F16
7 6
D7 D6
– If I/O is set for output (bit 6, Port Transfer Control Register = 0), data
written to the Port Data Register is latched and remains until new data is
written. The current data in the Port Data Register drives the port data bus.
If you read Port Data Register, the value read is the value last written to the
register.
– If I/O is set for input (bit 6, Port Transfer Control Register =1), the data read
from the Port Data Register is the data transmitted by the peripheral on
the port data bus. If you write to the Port Data Register, the data is latched
for output, but the data lines are not affected until I/O is again set for
output.
5 4 3
D5 D4 D3
Keysight E1458A Register Information
2 1 0
D2 D1 D0
131