Clyde Smith-Stubbs wrote:
>
> On Fri, Nov 12, 1999 at 10:10:38AM -0000, Andy David wrote:
> > The 18c series are the first PICs to have instructions that are > 1 word
> > long, hence it's possible to bypass the first word of the instruction
> > and execute the second on this family.
>
> True, but since the second word of the multi-word instructions is always
> a special kind of NOP, there's not much value in jumping into the middle
> of it.

The only value in this kind of code is to save a little bit of memory.  Usually
this is hardly necessary, but in the Apple ][, where I first encountered it,
all kinds of tricks like this were used to wedge in a couple more instructions.

I imagine that someone could do a short branch (one instruction) into the
second word of a two word instruction to "roll on" to the next instruction that
was just out of range of the branch.  I'm sure there are other tricks that
might be done with it, but it's unstructured and undebuggable code, to be used
only as a last resort.  In no way do I promote it, but in special cases a very
clever coder can get more out of the machine than the original designers of the
architecture ever suspected.

___________________________
|     Darrel Johansen     |
|     tempe,  arizona     |
|   darrelj@primenet.com  |
|_________________________|