On 2010-09-22 15:05, ivp wrote:
>>> operations other than 'clrf' on PORTx will/may produce a different
>>> result than the same operation on LATx
>>
>> Sorry, you're confusing me now!  How would MOVWF PORTx
>> and MOVWF LATx ever end in a different result?
>
> Bit operations like BCF/BSF to LAT are not the same as to PORT,
> because PORT does a read, so there is a possibility of read-modify-
> write errors

"PORT does a read" ? So does doing BCF/BSF on LATx also.
There is no difference in that way. BCF/BSF *always* reads.

And it's not only bit operations. There are a lot of instructions
that starts with a read of the FSR, AND/OR/XOR -WF, COM/INC/DEC -F
are some of them. They all have the same "problem".

*Any* operation that begins with a read of the actual FSR has
the same "problem". And that is, generaly speaking, all operations
whos result depends of the previous value of the FSR.

I think that CLRF and MOVWF are the *only* two operations that are
not depedning on the old value of the FSR, and are thus "safe" from
an R-M-W point of view since they do not read the FSR.

Jan-Erik.


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