Hi,

> 4 Input tied to ground.supply

> 4 Is free BUT can cause bad problems if software is changed.

    I would NEVER do that ! I have seen a product ( Thanks God it was not
mine ! ) from a client that just blew 200 boards in a cold month because of
that !!!! It was poorly designed in every way I can think of and was very
sensitive to EMI. The ports changed state from input to output and the chips
just blew apart. I agree that if the other aspects of the design were better
thought that should not happen often but I can't see any advantages of tying
the pin to ground !!

    Pull-ups or down are the best if you can afford it, if not just leave
the ports as outputs. There is nothing to be gained by relying on the
internal pullups or tying the pin to ground or VCC.

Best regards,
Alexandre Guimaraes

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