Now, *physicaly* the "skip" is always one
*program word*, not an "instruction" as such.

Yes, *practicaly* the code will run just as one
instruction was skipped, no matter if it was
an one-word or an two-word instruction.

So,

If the instruction following a skip is an
*one* word instruction, the second instruction
after the ship will be loaded and executed.
Just "as usual".
The skip will take one additional cycle.

If the instruction following a skip is an
*two* word instruction, the *second word*
of that instruction is loaded and executed.
Now, note that the encoding of *all* second
parts of all two-word instructions is such as
they will all be executet as a NOP, if they
are for some reason loaded as an instruction by
themself.
The skip will take *two* additional cycles (due
to the extra NOP executed).

Note that you can reach the second half of an
two-word instruction yourself if you add someting
to the PCL that makes the PC point to it.
It will then execute as an NOP, since that's the
encoding of all secons-parts of all two-word instructions.

An easy way to extend the instruction set with
two-word instructions... :-)

Jan-Erik.


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.
> 
> Thanks,
> - Marcel

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