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Entry type: FAQ Entry ID: 19039743, Entry date: 06/03/2004
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S5-95U: saving input information of the onboard I/O in the case of mains failure

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QUESTION:  
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?

ANSWER:  
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).

Note:
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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