Hi Randy

I've posted this code several times in this list, and got no comments on it.
I hope this help you

; Encoder read
#define encx    PORTA,1    ; Encoder inputs
#define ency    PORTA,2
;
;
; Inic (usually needless)
        clrf    auxint     ; Clear aux var
        btfsc   encx       ; and get encoder inputs
        bsf     auxint,0   ; in bit 0...
        btfsc   ency
        bsf     auxint,1   ; ...and 1
;
; Here starts the hard work
        movf    auxint,W   ; encod <- (actual state) xor (previous one)
        xorwf   encod,F    ; (only bits 0 and 1 affected)
;
        rrf     auxint,F   ; XOR results, reordered, get
        rlf     encod,F    ; into encod, in bits 0 and 1.
        rrf     auxint,F   ; This bits are the motion indicators
        rlf     encod,F
;
At this point you have a new read of the encoder. Bits 2 and 3 of 'encod'
have the information about the direction of movement of the encoder. If you
have to translate this information into a variable, then you can do
something like this:
;
        btfsc   encod,2    ; Direction 'X' motion
        incf    posenc,F
        btfsc   encod,3    ; ...or 'Y'
        decf    posenc,F
;
Bits 4,5 and 6,7 of 'encod' have the previous reads.

I place this routine in an time based interrupt (about 20ms time period).
The frequency of the interruption have to deal with the speed of the
incoming changes in the encoder signals.

Hope this helps,

ēlvaro.

----- Mensaje original -----
De: Randy A. <Cnc002@AOL.COM>
Para: <PICLIST@MITVMA.MIT.EDU>
Enviado: viernes, 01 de octubre de 1999 18:08
Asunto: Reading Quadrature Incremental Encoders


> Does anyone have information regarding how to read the Quadrature signals
> from an incremental encoder such as those used for feedback loops on servo
> motors on CNC machinery.  In fact I am working on a low cost controller
for a
> single axis machine.
>
> Any and all suggestions will be GREATLY appreciated.
>
> Randy A.
>