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  • BRX SD Card

    I have a bunch of string that are in retentive memory and its very important that the PLC never losses them. I have code that saves them to the SD Card on a Save Event and reads them on a Read Event.
    I'd like to automatically refresh them ONLY if the retentive memory was lost. Is there a system bit that will signify if the retentive memory has been lost?


  • #2
    ST149 $BatteryLow. When you power-up and that bit is ON, your retentive data is questionable.

    There is a super-capacitor that keeps the RAM state retained when the battery is low, but that is only for the purpose of replacing the battery (i.e. you have the battery in your hand, you power down the PLC, you replace the battery, you power back up). Super-capacitor retentive time is spec'ed in HOURs of time. Battery backup is spec'ed in YEARs.
    There are 10 kinds of people in this world, those who know binary, and those who do not.

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    • #3
      There really isn't anything directly available to the program. It gets logged. You could check ST1022. We set that when the clock has been set, and like everything, it gets cleared when there was a retentive memory failure.

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      • #4
        I think I'll issue a warning when the battery gets low and a option to restore the memory from the card when ST1022 gets cleared.
        I appreciate your help, thanks.

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