"
I am tracking the encoder position by interrupting on both rising and
falling edges of the XOR of A and B. In my interrupt routine, I compare the
current A and B to the previous A and B to determine which has experienced
a change and whether it is rising or falling. Based on this as well as
whether the other (unchanged) channel is high or low, I either increment or
decrement the count. I also take the gear ratio into account and compute
the correct motor shaft position."

The only thing I see you did not mention is you shifting the data over
before you xor.

This is the top end of my interrupt routine

ENCODER_INT_HANDLER
    CLRWDT                                                      ; HIT THE
DOG
    MOVF     PORTB, W                                           ; GET THE
NEW ENCODER DATA
    MOVWF    NEW_ENCDR                                          ; SAVE IT
    RRNCF    OLD_ENCDR                                          ; ROTATE OLD
DATA INTO POSITION
    XORWF    OLD_ENCDR, F                                       ; XOR TO GET
DIRECTION
    BTFSC    OLD_ENCDR,4                                        ; WHICH
DIRECTION DID IT GO IN?
    BRA      CLOCKWISE                                          ; CLOCKWISE
COUNTERCLOCKWISE                                                ; COUNTER
CLOCKWISE

Have you looked at the signal on a scope?


Tim




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