Mesa 7i76e I/O expansion via P1 / P2

Hello,

I build myself a small CNC Pendant which I would like to connect via P1 to my Mesa 7i76e.
In the documentation, it says that with the start of the Mesa card, every pin on P1 and P2 are Pulled Up to 5V and only register an Input when connected to GND.
Would it damage the Mesa 7i76e if I connect an NC switch to GND and an Input pin on P1?
It would cause the Input pin to be directly connected to GND at the start.

Does anybody already have experience in using P1 / P2 directly as inputs?

Best regards,
Floyd

That should be fine, just make sure the GND reference is from the P1 or P2 connector.

The most common cause of damage to bare FPGA inputs is from GND noise
that is, if you connect a bare FPGA input to frame GND, that GND may have 1-2V
of HF AC noise (from Motor drives etc) relative to the 7I76E GND, which will instantly
destroy the input clamp diodes.

Thanks for the quick response!

My plan was to use P1 as input pins (with P1 also supplying the GND and 5V reference) and then wire the pendant wheel into the MPG field input.
Or would it be possible to use an input of the P1 as an MPG input?

You could use software encoder counters (though these are limited by the ~1 KHz
servo thread sample rate, or firmware could be made with MPG encoder inputs

I think I will just use the dedicated MPG Inputs
Thanks again for the quick answers!