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Jinx wrote:
>> So the following is safe and will never introduce a transient?
>>
>> MOVLW B'100'
>> IORWF PORTB,F
> 
> I have a feeling that operations like IOR/AND/ADD/XOR etc would
> read the register first, leading to a possible r-m-w
> 
> You should be safe with BSF and MOVWF though. Particularly if the
> port contents are read into a buffer or shadow register, modified, and
> then written back with MOVWF

With respect to read-modify-write, BSF is not safe. BSF/BCF operate by
reading the port, altering the relevant bit, and writing the port. An
operation that definitively sets the value of every single bit (e.g.
movwf) is the *only* completely safe way to deal with RMW.

Chris
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