Siemens S7-300PLC scan cycle and timer problems - Database & Sql Blog Articles

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If the scan cycle of the program in the Siemens S7-300plc is 150ms, then it means that a series of stable clock timers with a period less than 150ms cannot be obtained, because one cycle needs to be longer than the clock.
A: The timer has a dedicated memory area. The timing of the timer is independent of the scan period of the system. That is to say, after a timer is enabled, the timer continues to run according to its own rules unless the enable signal changes or other related signal changes! After the operation is completed, the corresponding state is output, which does not change due to the change of the scan cycle, and only depends on its own conditions. In use, especially some friends who use STL programming sometimes encounter timers that are disobedient, which is actually related to our scanning. It is recommended that the timer enable and use programs do not jump, but scan every cycle. Because the so-called state in the PLC is actually determined by the RLO, and this thing is sometimes determined by the difference between the previous cycle and the latter cycle.