Chapter 2
Using Your NI 653X
2-2
ni.com
Controlling and Monitoring Static Digital
Lines—Unstrobed I/O
This section explains how to control and monitor static digital lines through
software-timed reads and writes to and from the digital lines of your
NI 653
X
.
Configuring Digital Lines
For unstrobed I/O, the direction of each of the 32 data lines is individually
configurable. You can configure each data line as one of the following:
•
Input
•
Standard output
•
Open-collector output
Standard Output
A standard driver drives its output pin to approximately 0 V for logic low,
or +5 V for logic high. Using a standard output driver has the following
advantages:
•
It does not require pull-up resistors.
•
It is independent of the state of the DPULL line, which selects whether
the 653
X
pulls the data lines high or low when undriven.
•
It has high current drive for both its logic high and logic low states.
•
It can drive high-speed transitions in both the high-to-low and
low-to-high directions.
Open-Collector Output
An open-collector output driver drives its output pin to 0 V for logic low.
For logic high, the output driver assumes a high-impedance state and does
not drive a voltage. To pull the pin to +5 V for logic high, a pull-up resistor
is required.
To provide a pull-up resistor, you can do one of the following things:
•
Connect the DPULL pin on the I/O connector to the +5 V pin. This
provides 100 k
Ω
pull-up resistors on all data lines. For more
information about CPULL and DPULL, refer to the
section of Appendix D,
.
•
Add a resistor to your circuit at the DUT.
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