I'm pretty sure you can find some example of that. Try searching using keyword ENCODER not decoder. Also it's not ABC, it's A B and Index.

You can also use PIC18F2331/2431/4331/4431. It has a quadrature decoder built-in the chip, called QEI module. Really nice to use with extra feature like noise protection. It's counting up or down according to A and B pulse, for CW and CCW rotation. Then you just have to read a register.


J-P