Insert The Back-Up Battery Or Rechargeable Battery - Siemens SIMATIC S7-300 Hardware And Installation Manual

Commissioning
9.4

Insert the back-up battery or rechargeable battery

Rechargeable battery and back-up battery for non maintenance-free CPUs
Rechargeable battery: If the CPU is operated without a back-up battery and you
only wish to back up the time against power failures on CPUs with a hardware
clock, you can insert a rechargeable battery in place of the back-up battery in the
back-up battery compartment. In this case only the time is maintained. The RAM
and RAM loading memory are not maintained in this case, so a memory card is
absolutely essential. A limited number (CPU-specific) of bytes may also be
maintained in a data block or by flags, timers and counters.
If you insert the back-up battery (buffered CPU mode), the RAM, the RAM loading
memory of the CPU and the clock are maintained even if the power fails. In this
case, all the data blocks and any flags, timers and counters defined in the
parameter settings are also maintained.
Exceptions
• The CPUs 31xC, 312, 314 (6ES 7314-1AF10-0AB0), 315-2 DP (6ES7315-
2AG10-0AB0) are maintenance-free and thus do not require a back-up battery
or rechargeable battery.
• CPU 312 IFM is not equipped with a back-up battery or rechargeable battery (it
is not buffered).
• The CPU 313 has a software, rather than a hardware, clock, so it does not need
a rechargeable battery (just a back-up battery is needed)
Inserting the back-up/rechargeable battery
Insert a back-up/rechargeable battery in the CPU as follows:
Note
Do not insert the back-up battery in the CPU until after POWER ON.
If you insert the back-up battery before POWER ON, the CPU requests a memory
reset.
1. Open the front panel of the CPU.
2. Plug the connector of the back-up/rechargeable battery into the corresponding
socket in the battery compartment of the CPU. The notch on the connector must
show towards the left hand side.
3. Insert the back-up/rechargeable battery into the battery compartment of the
CPU.
4. Close the front door of the CPU.
9-6
S7-300 Programmable Controller Hardware and Installation
A5E00105492-02