Abstract: The data bus and address bus in PC/104 is unattached, but in SJA1000, those are time-division multiplexing, the key of expand is how to cooperate the work timing between two computer structures. The paper anatomizes the operation timing of PC/104 and SJA1000, and finishes expand with just with two 47245 and some logic gates.With this expand, only one control sentence can achieve accessing between PC/104 and SJA1000. The method is new and unique， low cost and simple, and has been used in principle prototype of spaceflight optical remote sensor.

Key words: PC/104 Bus, CAN Bus, SJA1000