Siemens S7-300 Installation Manual page 117

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Is the correct mains voltage set for all component?
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Is the mains plug wired correctly?
Is mains voltage connected?
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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 power fails. In this case,
all the data blocks and any flags, timers and counters defined in the parameter
settings are also maintained.
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• &38  ,)0 is not equipped with a back-up battery or rechargeable battery (it
is not buffered).
• &38  has a software rather than a hardware clock, so it does not need a
rechargeable battery (just a back-up battery is needed)
S7-300 Automation System, Hardware and Installation: CPU 312IFM - 318-2 DP
A5E00203919-01
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