Ram Submodules With Battery Backup; Operational States - Siemens S5-155U System Manual

377 Memory Submodules
5.7.3
RAM Submodules with
Battery Backup

Operational states

Normal operation
5 - 58
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.
System Manual
C79000-B8576-C199-03