On Wed, 10 Sep 1997 13:53:23 -0400 "Martin R. Green" <elimar@BIGFOOT.COM>
writes:
>Because:
>
>   goto $       ; this is a continuous loop, hence
>   goto $-1    ; jumps to btfss   port,anotherbit
>   goto $-2    ; jumps to goto    action
>   goto $-3    ; jumps to btfsc   port,bit
>
>So there!   ;-)

It is worth mentioning 'goto $+1', which is effectively a NOP since it
just goes to the next instruction.  However, it takes 2 cycles instead of
1 as a NOP does.  This makes it useful for killing time a little more
efficiently if you need to waste a few cycles but not enough to justify
using a delay loop.  Another time killer is to label one of the returns
in the program and call it; this takes 4 cycles with one instruction.

This construct can be used to synchronize precisely to external events:
        btfsc   port,bit
        goto    $+1
It takes 2 cycles if 'bit' is low, and 3 if 'bit' is high.  There is a
trick to synchronize exatly to TMR0 based on this as well.