I really encourages you to use the USART. (which is the synchronous UART!) this way you don't have to deal with baude rates, etc, just connect tow micro controllers working at the same frequency, send data bytes from here to there, and build a routine to handle those data bytes.
I built that system with two 89s52's, and it worked perfectly, One of them was the master, and the other handeled all the line following and motor control issues, in the line follower robot (that you know about, since i was in the same university you are in now!!
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