In a message dated 10/2/99 3:46:23 AM Eastern Daylight Time,
morgans.rt@TELIA.COM writes:

> Matthew Ballinger wrote:
>  >     Or a much more efficient routine
>  Yes less instructions, but I have hard to see if it can beat an "addwf
PCL"
> in decode speed, once the input bits are retrieved, and we also have to
store
> them for next time.
>  But I will try your suggestion too.
>
>  >would be (in parallax mnemonics):
>  >ChkEncoder  mov new,encoder ;move the ra port the new var
>  >                 and     new,#00000011   ;clear all but encoder bits
>  >                 mov temp, new
>  >                 xor     temp,old        ;is old and new same?
>  >                 jz      :Return         ;if so quit
>  >                 clc                     ;clear carry
>  >                 rl      old             ;shift old to align old.0 with
new.
> 1
>  >bit
>  >                 xor     old,new         ;xor bits to determine direction
>  >                 jb      old.1,:up       ;if bit is 1 then up (CW,etc),
if
> bit
>  >is 0 then down (ccw,etc)
>
>  And then wee need to rotate the other way to align the other bits and xor
> them to see if it was up.
>  And if neither up or dn, and not same, both bits changed = overspeed or
> error.
>
>  Did I get it right?
>
    Not quite. *Everything* is taken care of with this code.
1.If code jumps to :return , then no change in posistion was made.
2.If the final xor produces a 1 then the encoder went CW
3.If the final xor produces a 0 then the encoder went CCW
Nothing more to do. Ok, well, add 1 instruction to store the old bits (oops).
Speed doesn't really suffer either. I'll count the instructions though to be
sure. You may be right.
Matt Ballinger