Better??, what is best depend on the application, sometimes economy is paramount, sometimes no. of port pins, sometimes speed sometimes something else. The better protocol you are asking for is totally hardware dependent, so I reply to "Does anybody know a better interconnect". I have used I2C (low cost, software overhead if uC does not have I2C interface, medium speed), Dual port memory (very fast, must be same board, somewhat expensive), 485 (distance tolerant, cost one driver chip, kinda slow), direct RxD to TxD connect (must be same board "kills" serial to the outside world) and in the olden days 232. I have not yet had the opportunity to use CAN, but it does look very good.