Troubleshooting Digital Output and Pulse Generation on the NI 9472, 9474, 9476 & 9475Hardware: CompactDAQ>>Digital Output Modules>>NI 9472
Problem: I can't seem to drive the digital outputs low on my NI 9472, 9474, 9476 & 9475. I also can't seem to generate a correct TTL pulse train on my NI 9472, 9474, 9476 & 9475, what could be the problem? Solution: When you set the outputs on the NI 9472, 9474, 9476 & 9475 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, 9476 & 9475 user Manual is shown below.  In order to interface the NI 9472, 9474, 9476 & 9475 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, as shown below. Related Links: Product Manuals: NI 9472/9474 Operating Instructions and Specifications Product Manuals: NI 9476 Operating Instructions and Specifications Product Manuals: NI 9475 Operating Instructions and Specifications Attachments:  Diagram1.png Diagram2.png - screenshotSmall.JPG
Report Date: 04/16/2007 Last Updated: 11/14/2008 Document ID: 48FAAMCW |
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