This document defines a recommended practice for implementing a bi-directional, serial communication link among modules containing microcomputers. This document defines those parameters of the serial link which relate primarily to hardware and basic software compatibility such as interface requirements, system protocol, and message format. The actual data to be transmitted by particular modules, which is an important aspect of communications compatibility, is not specified in this Recommended Practice. These and other details of communication link implementation and use should be specified in the separate application documents referenced in Section 3.1.