Implementing Class A Multiplexing Functions with Industry Standard Components

Multiplexing systems have been used in automobiles for the past decade. The use of these systems has allowed manufacturers to reduce wiring harness size, eliminate redundant sensors, and achieve a level of communication not available before. While most applications of multiplexing have been inter-modular communication, there exist many more opportunities to utilize multiplexing. These opportunities include multiplexing various user activated/interacted switches, sensors, and actuators. Multiplexing of this type is defined by the SAE as a low speed sensor/actuator bus, or Class “A” bus. The Class “A” bus addresses issues, such as: the challenge of handling increasing wiring complexity, incorporating diagnostics and testability into automotive electronic designs, facilitating the use of new switch and actuator technologies, and allowing a higher degree of systems design flexibility. This paper describes Chrysler's current multiplex bus system (a version of J1850), some of the Class “A” features of a vehicle, and explains the use of the HIP7030A2 (an industry standard J1850 IC) in a Class “A” bus. The performance of an assembled prototype Class “A” system will also be outlined. The prototype interfaces with typical automotive type switches and actuators using the HIP7030A2, and also interfaces with the J1850 bus. A comparison of a standard automotive switch system is made with a Class “A” Multiplex System utilizing the HIP7030A2.