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Why does my start trigger pin output 5 Volts?

I am trying to use the AI Start TRG input on my PXI system and am having problems. I have a PXI-6133 card with the TB-2709 SMB terminal connectors. I used this exact setup a few years back with a TTL pulse going into this AI START TRIG pin to trigger data capture. Now this same VI and hardware is not working. When I started diagnosing this, I determined that my AI START TRIG pin is putting out 5V. I am guessing this pin got switched to an output somewhere along the way, but I cannot find any way to set it back as an input. Has anyone seen this problem before, or know how to fix it? Thanks!

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How are you determining that the pin is outputting 5V? Is it through hardware or software?

Do you have other cards running on your chassis that could be setting that line to 5V?
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I am measuring the 5V output with a multimeter.


After digging some more through manuals I have found that this pin is supposed to be connected with a "weak" pullup. It is pulling 5mA of current when I ground this output, so it sounds like the pullup is 1k. 


I usually think of a weak pullup as more like 10k, so my external circuit to create the trigger pulse was not working. Now that I have adjusted the resistor values in my external circuit the trigger is working properly. 


I am still curious how to use this pin as an output signal if I want to send out a trigger pulse. I cannot find any way to change this pin from an input/output in Labview or in NiMax. Can you provide any suggestions on that?





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You could potentially create a clock output virtual channel in LabVIEW and use a property node to change the counter timebase source to that pin.

I haven't tested it out myself, but that could be something worth trying.

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