Overview

If a rising edge (0->1) of RESTORE is detected, then the first executed SFC section will perform the restore operation for all sections.

The all-at-once recovery is necessary to ensure that every SFC section gets back the stored StepIDs (internal identifier), even the disabled ones.

If a high signal is active at the RESTORE input, no SAVE and no RESUME will be performed, even if those inputs are active.

This is necessary to prevent overwriting the save area and to provide a clear separation of operating modes.

CLEARCHART / SETSTEP

To perform a RESTORE operation, a CLEARCHART will be executed.

This resets all steps and actions and also de-registers all SFC errors from diagnostic buffer.

After that, for each StepID taken from the storage area, a SETSTEP operation will be performed.

General Check

Before starting the RESTORE operation, a general check is performed to ensure integrity of the memory card data.

The application build ID must be equal and the version must be in valid range.

If not all of the checks succeed, the restore operation is aborted.

An error (An INIT was done due to restore error) is notified to EFB and diagnostic buffer.

NOTE: The PLC will not enter the HALT state. All SFC charts will start with INIT steps.

Individual Checks

There are also checks within individual sections:

  • save operation must be completed

  • the checksum must fit

  • StepID must be valid

If an error occurs during recovery of individual sections, then the SFC section currently in progress is forced to the initial state.

A warning (Not all SFC charts could be restored / resumed / initialized) is notified.

Detecting such failures will not prevent the complete restore mechanism to restore as much steps as possible.