In some cases a user may need to resume operation based on machine values from a previous running state after power up. This is typically achieved with the use of a CPU mounted battery unit. The CP1E-N type PLC offers a backup battery as an option while the CP1E-E type PLC does not offer the option to mount a battery. Use an CP1E-N type CPU Unit with a battery mounted if it is necessary to retain the contents of the DM Area (D) and Holding Area (A), the Counter Present Values (C), the status of Counter Completion Flags (C), and the status of bits in the Auxiliary Area (A) related to clock functions when the power supply is turned ON after the power has been OFF for a period of time. These contents and status cannot be retained with an CP1E-E-type CPU Unit. However, the CP1E CPU Unit does offer a DM Backup Function that saves specified words from the DM Area to the built-in EEPROM backup memory area.

Using DM Backup Function on CP1E

Specified words starting from D0 in the built-in RAM can be saved to the built-in EEPROM backup memory by turning ON A751.15. (These words are called the DM backup words and the data is called the DM backup data.) A751.15 (DM Backup Save Start Bit) can be used in any operating mode (RUN, MONITOR, or PROGRAM mode).
 

*Notes:
1. The clock cannot be used if a battery is not installed or the battery voltage is low
2. The contents of the DM Area (D) will become unstable if the power supply is interrupted for longer than the backup time of the built-in capacitor (50 hours for an CP1E-E-type CPU Unit, 40 hours for an CP1E-N-type CPU Unit without a Battery)
3. The ERR/ALM indicator on the front of the CPU Unit will flash when the Battery is nearly discharged
4. The Battery Error Flag (A402.04) will turn ON only if the Detect Low Battery parameter in the PLC Setup has been set to detect a low-Battery error for the CP1E-N type CPU Unit
5. This article was written in July of 2010 and the information contained is based on hardware and software features at that time. This information is subject to change
6. See CP1E User Manual W480 for more details on the procedure, section 16-3