On Wed, 9 May 2007 12:31:34 -0700, "Marcel Birthelmer" wrote:

>Hi all,
>I have a question regarding to consecutive btfsX statements.
>For example:
>
>btfss REG, 0
>btfss REG, 1
>bsf REG, 2
>
>now obviously when REG,0 is 0 then REG,1 is evaluated as expected, but
>what happens if REG,0 is 1? Is bsf REG,2 executed, or is it evaluated
>as a NOP?
>
>The processor is an 18F452, though I'm not sure that's relevant. I
>checked the description for BTFSS, and it says that if it's a "skip"
>followed by a 2-word instruction, it is followed by 2 NOPs. But does a
>conditional followed by a 1-word instruction become a 2-word
>instruction? I think not, but I'm not sure.
>

In the 18F chips, the second word of all two-word instructions is
always executed by itself as a 'nop'. If it weren't, using the 'btfsc'
and 'btfss' instructions would be so unpredictable as to be useless.

That doesn't really matter since that second btfss instruction is a
one-word instruction anyway. 

If bit 0 of REG is set, the "btfss REG, 0" instruction will skip the
following instruction, the "btfss REG, 1", and execute the 'bsf'
instruction.


Regards, Bob

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