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在工业控制中常采用“一主多从”这样上位机控制下位机的方式实现远程监控,这一方式由于受串行异步通信方式的制约,用软件编程的方法,分布在RS485串行总线上的多个不同PLC(下位机)的相关DO点无法做到一次性闭合或者断开。针对这一问题,文章提出了一种采用硬件联馈与软件配合的方法,通过在PLC上专门分配用于同步信号输出的DO点,并将这些点与需要同步动作指令的DI点用导线直接连接,再通过PLC程序的配合,最终简单而有效地解决了这一问题。最后结合实例给出该方案的具体硬件、软件实现方法。
In industrial control often used “a master and more from” such a host computer to control the way the lower the remote monitoring, this method due to the serial asynchronous communication mode constraints, with software programming method, distributed in the RS485 serial bus A number of different PLC (lower computer) related to the DO point can not be a one-time closed or disconnected. In response to this problem, the article presents a method of using hardware and software with the software through the PLC dedicated distribution for the DO signal synchronization output, and these points and the need for synchronous action command DI point direct wire Connection, and then through the cooperation of the PLC program, the final simple and effective solution to this problem. Finally, the specific hardware and software implementation of the program are given with examples.