I am now occouring a FPGA pin damage problem.

One of my pin is hardware connected to a 1.8V signal that will be switched on/off occasionally, while the port is not connected to any other logic gate in my FPGA, so the input pad is FPGA internal folating.

And this structure seems to damage my FPGA input port, the input resistance decreased from infinite to hundreds Ohm after some time.

I also have another test that the input pin directly feeds the signal to a FPGA otput pin, in this case, it seems to work perfactly so far.

So, I was wondering, will an internal floating input port damaged by external signal easier than those connected ones?

When I searched "pin" "floating", it always came out with external floating related results, plus an "internal" key word does not really help, so I am here to ask you for help.


  • \$\begingroup\$ Where did you get the term "FPGA internal floating" from? \$\endgroup\$ Nov 26, 2015 at 2:11
  • \$\begingroup\$ Most FPGAs do not support internal tristates, so it's not possible for a pin to be floating inside the FPGA. And even if it was, it should not affect the actual pin. Generally the only things that you can tristate are the I/O pins themselves via the I/O banks. Internal 'tristates' are generally just implemented as multiplexers. \$\endgroup\$ Nov 26, 2015 at 7:12
  • \$\begingroup\$ And how precisely are you trying to measure the "input resistance" of a port? \$\endgroup\$
    – user39382
    Nov 26, 2015 at 8:10
  • \$\begingroup\$ Hi Tom: I am using that phrase because I assigned an input port, and left it there. I did not use that input/pin in any other statement. \$\endgroup\$ Nov 26, 2015 at 8:46
  • \$\begingroup\$ Hi Alex: Sure, as you said, I was focus on the input port only. And being honest, I have to check the tristate stuff you mentioned. \$\endgroup\$ Nov 26, 2015 at 8:58

1 Answer 1


Do you have a grounded anti-static mat and wrist strap?

If you have a floating pin not connected to anything else, it is much more susceptible to electrostatic discharge (ESD). That may well show as a resistance to ground in the 100s of ohms.


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