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Troubleshooting Digital Output and Pulse Generation on the NI 9472/9474

Hardware: CompactRIO>>Digital Output Modules>>NI 9472

Problem:
I can't seem to drive the digital outputs low on my NI 9472/9474. I also can't seem to generate a correct TTL pulse train on my NI 9472/9474, what could be the problem?

Solution:
When you set the outputs on the NI 9472/9474 to High or Low, the channel does not toggle between VSUP and COM as some people might expect. It actually toggles between VSUP and a high impedance state. A diagram from the NI 9472/9474 User Manual is shown below.

In order to interface the NI 9472/9474 with a device expecting VSUP or 0 volts (like the 9411), you must use pull-down resistors to pull the high impedance lines to ground. A standard value of 10 kOhm should work in most cases.

Related Links:
NI 9472/9474 Operating Instructions

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Report Date: 04/16/2007
Last Updated: 05/23/2007
Document ID: 48FAAMCW

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