Siemens S5-135U, System Manual

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5-85
System Manual
C79000-G8576-C199-06
5.10.3 RAM Submodules with Battery Backup
RAM submodules with battery backup are used when the contents of the
memory submodules must be retained even outside the CPU. You can then
remove the battery-backed 377 memory submodule from the CPU without
loss of data. An integral battery protects the submodule from data loss, and
ensures that the data will be retained until the RAM submodule is used again.
Note
The RAM submodule with battery backup is not a substitute for an EPROM
submodule. The contents can be overwritten by a STEP 5 program. The
battery can discharge if the submodule is at standby for a long time. This can
result in the loss of data.
To protect the battery, the 377 memory submodule has a cover on both sides.
The button cell battery with terminal lugs is secured on the submodule with
screws on two holders. When the grip is swivelled in, you can see the battery
fault LED.
There are three different operational states for the RAM submodule with
battery backup:
In this state
the battery-backed RAM submodule is in the CPU;
the programmable controller (PLC) is switched on (Power On);
and neither the backup battery of the PLC nor the battery of the RAM
submodule is supplying power.
Note
The RAM submodule must not be inserted or removed during the RUN state;
this can result in data corruption, loss of data or CPU malfunctions.
Operational States
Normal Operation
CPUs, Memory Cards, Memory Submodules, Interface Submodules