Dave and Sandy Thomas <PICLIST@MITVMA.MIT.EDU> wrote:

> ; delay 1 millimeter = 6 microseconds = 12 cycles at 8.0 MHz
> rdloop:
>         incf    range,1         ; 0 increment range
>         btfsc   status,zf       ; 1
>         incf    range+1,1       ; 2
>         movf    range+1,w       ; 3 test for timeout - 10752 mm
>         xorlw   (maxrange/256)+1        ; 4
>         btfsc   status,zf       ; 5
>         goto    rddone          ; 6
>         btfss   portb,echo      ; 7 test for echo
>         goto    rdloop          ; 8
> rddone:
>
> My calculations agree that echo transit time is approximately
> 6 microseconds per millimeter (3 microseconds one way).  But
> I count only 10 cycles per loop--so does MPSIM (under MPLAB).

    Dave:

    You and MPSIM are correct; the loop takes 10 cycles per
    iteration (except for the last time through, of course, when it
    takes either 8 or 9).

    -Andy

Andrew Warren - fastfwd@ix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499