Operator control (hardware)
3.3 Memory concept
3.3.4 Power off behavior
Power failure
During a power failure, the data in the SRAM of the control unit are backed up by an internal
SuperCap and the optional fan/battery module.
The nonvolatile data are available for the next startup. Thus, the control unit is immediately
operational without data loss.
Saving lastest state
On the system side, it is ensured that the latest consistent overall image of the nonvolatile
data is always available the next time the unit is powered on even if there is a power failure
during backup with the _savePersistentMemoryData system function.
The system accomplishes this by renaming an existing backup file as the backup copy of the
backup file and then performing the actual backup in the backup file.
During startup, the associated data quality is indicated by the
persistentMemoryPowerMonitoring. PersistentDataState system variable. If the backup
operation was interrupted by a power failure, and the backup file is thus inconsistent, the
backup copy of the backup file (i.e., the most recent consistent version) is used, and the
system variable signals this accordingly.
D4xx
3-16 Manual, 12.2004, 6AU1900-1AJ32-0BA0
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