Hi Buzz,

Assuming you're talking about an incremental (relative) shaft encoder (with the standard A-B quad. outputs), it's fairly easy to do. Where the problems start to arrise is when you're using a high resolution device (500ppr or more), then the 8051 would need to monitor quite high frequencies if the shaft is to turn at even a reasonable speed.

Are you using the encoder for user input (like a data wheel), or are you using it in some kind of positioning system?

Matt.