In a message dated 10/3/99 6:08:38 AM Eastern Daylight Time, 
morgans.rt@TELIA.COM writes:

> Well.. To be safe, the routine has to detect also when both phases has 
> changed (180¡ cycle rotation since last time)  This will indicate overspeed 
> or hardware error, noise or other error.  

In a hardware error, most likely 1 or both outputs would not change at all.

>W often has to now when/if the 
> routine fail so we dont tahe an erroneous cont for correct, especially in 
> machine positioning...
>  

ChkEnc  mov new,Enc     ;get new input
    and new,#%00000011  ;get rid of all but 2 enc bits
    mov temp,new    ;make copy
    xor temp,old    ;is old = new
    jz  ChkEnc      ;then no change, go back
    cje temp,#3,err ;goto "error" if both bits changed
    clc         ;get ready for right shift
    rl  Old     ;align bits
    xor old,new     ;check for direction
    jb  old.1,up    ;if 1 then up direction, if 0 then down direction

    Error detected! I use scenix chips at 50-85MHz.The chances of missing a 
change are slim, however. As long as it is scanned every 1/(resolution of 
encoder*max changes per sec).
Matt Ballinger