DSA-MTR-12A2
DSA-MTR-12A2
DSA-MTR-12A2
在西门子S7-400plc内，FB块调用FB块，PLC循环扫描时，被调用的FB块是如何被执行的，包括内的静态变量、临时变量是如何被扫描的啊，静态变量什么时候被存储到背景数据块啊，我看到有段程序，被调用的FB块内部输入变量在监控时一直在变化，而调用他的FB块外部输入条件一直不变，这是为什么？
答：PLC的扫描机制是从上而下，自左向右顺序扫描。有中断就去执行中断程序的内容。中断又按优先级扫苗。
无论你是怎么调用FB的，（多个FB调用同一FB或同一FB调用多个FB），PLC的CPU都是顺序扫描，当你调用的条件满足了，就执行调用功能，这个时候的FB外部管脚填写的相应变量，和内部临时变量（执行完这个FB功能，temp变量自动释放）和静态变量，是这个时候，调用这个FB的情况满足条件下的数据。
PLC接着顺序扫描，在下面又调用同一个FB，那么这个时候的外部管脚填写的变量，和内部的临时变量（（执行完这个FB功能，temp变量自动释放）和静态变量，是这个条件满足下的执行的FB功能，那么就会覆盖上面一个调用同一个FB的，外部管脚变量和静态变量。
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