The paper introduces a kind of interface software design method based on RS 422A, its operation principle, and software reliablity design and implementation procedure on the target prototype are discussed, and establishes a useful communication mode of the master slave relation. 介绍了一种基于RS-422A的接口软件设计,讨论了它的工作原理及在目标样机上软件可靠性设计的实现过程,建立了一种适用于主从关系的通信模式。