Andrew Warren wrote:
>Morgan Olsson <PICLIST@MITVMA.MIT.EDU> wrote:
>
>> You may also byte-write (movwf and clrf) to port B without
>> disturbing interrupt on change, just do not do any kind of reading
>> except for the one instance in interrupt routine. (Remember that
>> BSF/BCF actually begins by executing a read...)
>
>Morgan:
>
>No, you can't avoid reading PORTB by using MOVWF, CLRF, etc.
>
>EVERY instruction that accesses PORTB reads it; the "write"
>instructions just throw away the values that they read.
>
>-Andy

In practice that seem not to be the case.  Can you give some pointer to an document describing movwf and clrf doing reads?

In my current project I frequently move debug information out on port B (using the lowest three bits set as outputs) both during interrupt and in main, and I have never observed any side effects.

/Morgan

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