Restoring and Backing Up Projects

The CPU application RAM and the CPU flash memory automatically and manually perform the following:

Restore a project in the CPU from the flash memory (and the memory card if inserted):
- Automatically after a power cycle
- Automatically on a warm restart
- Automatically on a cold start
- Manually with a Control Expert command: PLC → Project Backup → Backup Restore
NOTE: If a memory card is inserted with a different application than the application in the CPU, the application is transferred from the memory card to the CPU application RAM when the restore function is carried out.
Save the CPU project in the flash memory (and the memory card if inserted):
- Automatically after an online modification is performed in the application RAM
- Automatically after a download
- Automatically on detection of %S66 system bit rising edge
- Manually with a Control Expert command: PLC → Project Backup → Backup Save
NOTE: Backup begins after the completion of the current MAST cycle and before the start of the next MAST cycle.

Because MAST is configured as periodic for all Hot Standby CPUs, set the MAST period to a value larger than the actual MAST execution time. This lets the processor complete an entire backup without interruption.

If the MAST period is set to a value less than the actual MAST execution time, backup processing is fragmented and requires a longer time to finish.
Compare the CPU project and the flash memory project:
- Manually with a Control Expert command: PLC → Project Backup → Backup Compare
NOTE: When a valid memory card is inserted with a valid application, the application backup and restore operations are performed as follows:
- The application backup is performed on the memory card first and then on the flash memory.
- The application restore is performed from the memory card to the CPU application RAM first and then copied from the application RAM to the flash memory.