The Class A Task Force of the Vehicle Network for Multiplex and Data Communications Committee is publishing this SAE Information Report to provide insight into Class A Multiplexing. Multiplexed actuators are generally defined as devices which accept information from the multiplexed bus. A multiplexed actuator can be an output device controlled by the operator or an intelligent controller. A Multiplex actuator can also be a display device that reports the status of a monitored vehicle function. This document is intended to help the network system engineers and is meant to stimulate the design thought process.

A list of multiplexed actuator examples is provided in Appendix A, Figure A1. Many other examples can be it identified.

Three Classes of Multiplex Networks

The Vehicle Network for Multiplex and Data Communications Committee has previously defined three classes of vehicle data communication multiplexing: Class A, Class B, and Class C. A hierarchical relationship exists between the three classes. Class A multiplexing is a subset of Class B and Class B multiplexing is a subset of Class C. Definitions of all three classes are included in this document for reader convenience.

A Class Multiplexing

Class A Multiplexing contains many of the direct operator controlled functions and the displays monitored by the operator. Some examples of actuator outputs would be the operator control of powered convenience features such as power windows, door locks, and windshield wiper.

B Class Multiplexing

Class B Multiplexing provides the data communications between different modules, internal and external to the vehicle, for the purpose of sharing common data about the vehicle. An example of this is the diagnostic information shared between an internal (on-vehicle) module and an external (hand-held) module for service repair.

C Class Multiplexing

Class C Multiplexing is used for real-time high-speed control, and normally requires a significant amount of data communication to function properly. An example is the hydraulic actuator for the Anti-Lock Brakes System.

Analog as Well as Digital

The physical transportation of the information in a Class A Multiplex application can use analog or digital techniques. The information can be transported by an encoded voltage, resistance, or other physical value impressed on the transportation media. The transportation media can be a wire, but is not limited to a wire. In some cases, it is difficult to identify an actuator as digital or analog. For example, a stepper motor can be used to control a flapper position in a heat exchanger. Although the motor has digital control, the intent of the control is analog as perceived by the vehicle operator. Hence, the Class A application of the flapper is identified as an analog function. In contrast, a door lock is a digital function. This concept is discussed further in the document.