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Entry type: FAQ Entry ID: 19039743, Entry date: 06/03/2004

S5-95U: saving input information of the onboard I/O in the case of mains failure

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How can the input information of the onboard I/O be saved securely in the case of power failure so that it is available again when the power returns?

Using the diagnostics byte (EB35) you can securely save information that has not been saved at the inputs of the onboard I/O at the time of the power failure. The onboard supply is monitored with Bit 2 of the EB 35 (all power supply connections). You can use a link to this input bit in the user program to back up the status of the inputs of the onboard I/O.

Diagnostics byte
The diagnostics byte provides you with the following options for checking the running of the process:

  • Counter overflow.
  • Whether and where an alarm has been triggered.
  • Whether power supply for the onboard I/O has failed (only S5-95U) - only if all the 24V power supplies have failed. 
    The ground is common to all inputs/outputs; they are non-floating.
    • Pin 1b - (L+) for inputs I32.0 ...I33.7
    • Pin 1a - (L+) for outputs Q32.0 ...Q32.7
    • Pin 11a - (L+) for outputs Q33.0 ...QA33.7

    If at least one of the (L+) 24V  power supplies given above is available, then the "Power failure for onboard I/O E35.2" bit is "0".

  • Whether the batter backup is available (only S5-95U).

More information is available in the "S5-90U/S5-95U Programmable Controller System Manual" in Entry ID: 1091648.

  • Chapter 5 Diagnostics and Troubleshooting - Diagnostics byte
  • Section 3.3.5 Connecting the Onboard I/Os of the S5-95U 
    Fig. 3-22 Wiring of the Front Connector for Digital Inputs and Outputs

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