On Thu, 6 Jun 2002, Joe Farr wrote:

>If you present a value to say port D on a 16F877 and then change the
>value of just one of port D's bits, do the other bits 'glitch' i.e.
>possibily, under really strange circumstances, like a full moon maybe,
>even just for a nano second, change their logic state before returning to
>their previous state ?
>
>If you send a value '0x00' and then '0xFF' to a port, do all the bits
>change at the same time ? I'm assuming the answer is yes to this one...

Not quite. It depends if the loading is identical (capacitive loading
esp., or inductive, as in long unequal wires). When this is not the case
then the edges of adjacent outputs are within 50ns of each other (16C54 @
4MHz).

However if you use code like:

  bcf   PORTD,Abit
  btfsc Somereg,Someflag
  bsf   PORTD,Abit

then you have a glitch factory in your code. The same thing applies if the
outputs are heavily loaded and you use rmw instructions on PORTD.

Peter

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