Andy David wrote:

> - 16 cycles
> - 16 words

  17 if you want to reverse two bytes at once.

> - Enter with byte to be reversed in WREG, ends with reversed byte in
> WREG.

  No, it ends with the reversed byte in W, not WREG as written, or in
Reverse if you specify F as destination.  Unless you're talking of a PIC
with which I'm not familiar.

> - Isochronous.
> 
>    rlf    WREG,f          ; WR  = d6 d5 d4 d3 d2 d1 d0 C  {C = d7}
>    rrf    Reverse,f       ; Rev = d7 R7 R6 R5 R4 R3 R2 R1 {C = R0}
>    rlf    WREG,f          ; WR  = d5 d4 d3 d2 d1 d0 C  R0 {C = d6}
>    rrf    Reverse,f       ; Rev = d6 d7 R7 R6 R5 R4 R3 R2 {C = R1}
>    rlf    WREG,f          ; WR  = d4 d3 d2 d1 d0 C  R0 R1 {C = d5}
>    rrf    Reverse,f       ; Rev = d5 d6 d7 R7 R6 R5 R4 R3 {C = R2}
>    rlf    WREG,f          ; WR  = d3 d2 d1 d0 C  R0 R1 R2 {C = d4}
>    rrf    Reverse,f       ; Rev = d4 d5 d6 d7 R7 R6 R5 R4 {C = R3}
>    rlf    WREG,f          ; WR  = d2 d1 d0 C  R0 R1 R2 R3 {C = d3}
>    rrf    Reverse,f       ; Rev = d3 d4 d5 d6 d7 R7 R6 R5 {C = R4}
>    rlf    WREG,f          ; WR  = d1 d0 C  R0 R1 R2 R3 R4 {C = d2}
>    rrf    Reverse,f       ; Rev = d2 d3 d4 d5 d6 d7 R7 R6 {C = R5}
>    rlf    WREG,f          ; WR  = d0 C  R0 R1 R2 R3 R4 R5 {C = d1}
>    rrf    Reverse,f       ; Rev = d1 d2 d3 d4 d5 d6 d7 R7 {C = R6}
>    rlf    WREG,f          ; WR  = C  R0 R1 R2 R3 R4 R5 R6 {C = d0}
>    rrf    Reverse,w       ; W   = d0 d1 d2 d3 d4 d5 d6 d7 {C = R7}

; 17th instruction tidies everything up:
     rlf    WREG,f          ; WR  = R0 R1 R2 R3 R4 R5 R6 R7 {C = C¡}
-- 
  Cheers,
        Paul B.