从上面描述的主程序接口及中断程序接口，我们可以看出：操作系统是PLC的大管家，是它控制着用户程序的执行及中断的响应。其实，PLC的操作系统在执行用户程序之前，还要做一些其它工作，如下图：PLC在冷启动或热启动后，会执行启动扫描。在这个步骤中，可以对一些变量进行初始化。启动扫描仅在每次启动后执行一次，在S7-...
在讨论PLC的工作原理之前,我们先来看看PLC的程序结构。 PLC的CPU中有两类程序:一类是操作系统,它由PLC的厂家设计并在出厂前固化到CPU中;另一类是用户程序,它是由编程人员根据实际需要设计的、完成特定功能的程序; 操作系统预留一些接口(Interface)给用户程序。通过这些接口,操作系统可以控制用户程序的执行。一般有两...
PLC的循环扫描 PLC在冷启动或热启动后,会执行启动扫描。在这个步骤中,可以对一些变量进行初始化。启动扫描仅在每次启动后执行一次,在S7-300/400系列PLC中,OB100(暖启动)、OB101(热启动)和OB102(冷启动)是用于启动扫描的组织块。 启动扫描完成后,PLC进入循环扫描的阶段。首先进行内部检查,然后将外部的数字量输入...
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PLC的CPU中有两类程序:一类是操作系统,它由PLC的厂家设计并在出厂前固化到CPU中;另一类是用户程序,它是由编程人员根据实际需要设计的、完成特定功能的程序; 操作系统预留一些接口(Interface)给用户程序。通过这些接口,操作系统可以控制用户程序的执行。一般有两种接口:主程序接口和中断程序接口。
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Two years working experience in automation maintenance, master AB-PLC of how it works, you can write AB-PLC program and host computer screen, to installation site and process automation equipment. About Siemens plc, Siemens PLC can write a simple program. English, simple English. ...
If you are starting out, learning PLC programming, you should just care about the scan time. Reading the I/O, then executing your program and at last updating, the I/O is a good fundamental understanding of how a PLC works. When you are starting out learning PLC programming, knowing abou...
Forming a Conglomerate Acquisitions:When one company buys another company, it is anacquisition. If a target firm is big enough, it might not become a mere subsidiary; instead, it and the acquiring company mightmerge, combining their talent, assets, resources, and personnel into one new legal ...
Learn PLC Programming - Without a PLC! The programming environment and I/O connections are the two main areas in which a PLC stands alone compared to all other microporocessor-based platforms. If these two obstacles could be solved, there would be no shortage of low-cost PLC trainers for ...