If you have the pins available and the inclination to do so you could try setting up your own protocol to interface to microcontrollers. I have seen a project where the developer wrote his own code for exchanging data between two uCs, with his own handshake signals.

If you want serial communication you need 3 pins, if parallel, you'd need 1 port + 2 pins (a minimum of 2 handshake lines would be needed)

the 8051 has its own variable baud rate serial communication facility. why not use that?

Kundi