I forgot to say yesterday, another choice worth looking into is of course, the CAN bus!

There are numerous 8052 microcontrollers made by several manufactures with build in CAN controllers now. I have no experience in using CAN, but from what I have read, it seems to be ideal for the kind of application you are working on. I seems to require quite a bit of reading up on and playing with to get an understanding of how to use it. I haven't had the time yet, or the need to be honest.

Matt.