1. An interface circuit for automatically providing bi-directional communication with at least one on-board vehicle computer under a plurality of different communication protocols, comprising: bi-directional communication means for enabling communication under a first communication protocol; full duplex communication means for enabling communication under a second communication protocol, said full duplex communication means having a receive bus and a complimentary transmit bus; edge-detect means for distinguishing between identification data and communication data, said edge-detect means having an input; comparator means having a first input for receiving a voltage reference, a second input for receiving a data input and an output coupled to said input of said edge-detect means, said comparator means and edge-detect means changing a mode of communication between said first communication protocol and said second communication protocol; and feedback means coupled to the bi-directional communication means for enabling reception of incoming messages while filtering a local echo of a transmitted message.