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Chapter 4
Signal Connections
©
National Instruments Corporation
4-9
DAQCard-DIO-24 User Manual
computer. Notice also that any current drawn from this line adds to the
power requirements from the computer.
Timing Specifications
This section lists the timing specifications for handshaking with the
DAQCard-DIO-24. The handshaking lines STB* and IBF synchronize
input data transfers. The handshaking lines OBF* and ACK*
synchronize output data transfers.
The following signals are used in the timing diagrams on the subsequent
pages.
Table 4-4.
Signal Descriptions
Signal
Direction
Description
STB*
Input
Strobe Input—A low signal on this handshaking line loads data into the input
latch.
IBF
Output
Input Buffer Full—A high signal on this handshaking line indicates that data
has been loaded into the input latch. This is an input acknowledge signal; a low
signal indicates that the latch is ready for another input.
ACK*
Input
Acknowledge Input—A low signal on this handshaking line indicates that the
data written to the selected port has been accepted. This signal is a response
from the external device that it has received the data from the
DAQCard-DIO-24.
OBF*
Output
Output Buffer Full—A low signal on this handshaking line indicates that data
has been written to the selected port
INTR
Output
Interrupt Request—This signal becomes high when the DAQCard-DIO-24
requests service during a data transfer. The appropriate interrupt enable bits
must be set to generate this signal.
RD*
Internal
Read Signal—When this signal is low, data is transferred from the
DAQCard-DIO-24 to the CPU. This signal is generated from the control lines
of the computer.
WR*
Internal
Write Signal—When this signal is low, data or control words are transferred
from the CPU to the DAQCard-DIO-24. This signal is generated from the
control lines of the computer.
DATA
Bidirectional
Data Lines at the Selected Port—This signal indicates when the data on the data
lines at a selected port is or should be available.
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