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TH1 Communications to C more panel

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  • TH1 Communications to C more panel

    My understanding is that there is a bump in processor scan time caused by ethernet communications. This can be mitigated by a POM card. What about serial communications to a Cmore, does that influence scan time? In this application Cmore can be updated every 2 seconds or more, But the PLC should be able to do the main software at a steady scan rate of 10 msec.


  • #2
    The largest bump to the scan time is definitely Ethernet and the IP stack. The POM back end is a serial port (regardless of the front side port), and the scan bump to service it is significantly lower. Serial comms don't impact that scan much.

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    • #3
      great answer Bob O. And I see where I can set serial comis to once every 500ms and so help keep scan time steady.

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      • #4
        The communication is performed by a serial periferal device with DMA access to shared memory. If many or large data blocks need transferred, the cpu of the plc is responsible only to read/ write into shared memory, while the periferal transfers data. In that situation, the machine cycle needs interrupted to allow data transfer.
        the main purpose of a plc is not to communicate. It is instead to read and write io tables.
        Communication can not replace io signals. It takes few milliseconds for an io signal to get through and while Ethernet comms can be even faster, the delivery time can not be guaranteed. For this reason, communications only relate to slow changes in machine state like a temperature or a servo offset, but can never relate to an emergency stop.

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