With the increasing use of electronic control systems to improve vehicle dynamics, there is an ever growing need to transfer control information among electronic control units(ECUs). To meet this need, a protocol was proposed for high-speed multiplex in the previous SAE paper 910463. Based on the paper, a prototype IC for high-speed multiplexing control was developed.First, a further analysis was made of the information which is transferred among ECUs. As a result, it was found that the information has certain distinctive characteristics. These characteristics are so distinctive that it may be relevant to devise a new protocol for communication.Based on the analysis, a new form of token passing method was implemented. By using this method, it is easy to calculate transmission latency time. So this method is suitable for a real time control application like vehicle dynamics control.Another key point of high-speed data communication is the extent of load imposed upon the host microprocessor. Although a serial communication interface was used, by using methods of ID filtering, ID sorting, and DMA, the load on the microprocessor was made very light.