Controlling And Monitoring Static Digital Lines-Unstrobed I/O; Configuring Digital Lines; Standard Output; Open-Collector Output - National Instruments 653 Series User Manual

Chapter 2 Using Your NI 653X
Controlling and Monitoring Static Digital
Lines—Unstrobed I/O

Configuring Digital Lines

NI 653X User Manual
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 653X.
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 653X 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 kΩ 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.
Hardware Considerations.
2-2
Power-On State
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