中文摘要：

研究了RS232C协议接口电气特性和DCS系统网络的工作特性，分析了基于RS232C协议的并发呼叫帧发生碰撞的机理及由并发碰撞引起的帧错误类型。引入了泊松流以描述系统中的多主呼叫过程，建立了基于RS232C串行通信协议的并发帧碰撞模型。呼叫帧格式、传输速率和呼叫密度共同决定了发生帧碰撞的概率。平均呼叫密度小于10次／s时，发生帧碰撞的概率小于0．01％，并可以被多主呼叫策略所标识，连续2次呼叫失败的概率小于0．0001％，试验表明：基于RS232C的多主呼叫协议是可行的，为即插拔多主RS232C通信协议设计提供了理论依据。

英文摘要：

The circuit and topology of RS232C interface are analyzed to reveal the mechanism of multiple callings from terminals. Poisson distribution is introduced to describe the calling process and develop the collision model. A collision probability depends on calling frame format, baud rate and calling frequency. The collision probability of calling from two or more terminals is less than 0.01% when mean calling frequency is less than 10 times per second. The collision can be listened, identified and compensated with another calling, whose collision probability is less than 0.000 1%. It is showed that the communication strategy of multiple terminals calling to central computer with RS232C protocol is feasible.