Standby operation
In this standby state of the unit
••
the battery-backed RAM submodule is in the CPU;
••
the PLC is switched off (Power Off);
••
the backup battery of the PLC is providing backup of the RAM
submodule;
••
the submodule battery is not supplying power.
Note
It is only possible to insert and remove the RAM submodule in
this state without data corruption.
If the backup battery in the PLC fails in this state, the submodule
battery provides backup of the RAM submodule. This prevents loss of
data.
Submodule standby
In this standby state of the submodule
••
the RAM submodule has been removed from the CPU;
••
the submodule battery is providing backup of the RAM submodule;
••
the contents of the battery-backed RAM are retained.
Battery monitoring and
battery fault
The battery of the battery-backed RAM submodule is monitored.
When the RAM submodule goes to normal operation (battery-backed
RAM is in the CPU, supply voltage of the PLC is switched on), the
battery monitor on the submodule detects the following faults:
••
Submodule battery is not present.
••
Submodule battery is faulty (voltage less than 2.6 V).
The red battery fault LED on the front of the submodule is
continuously lit.
Note
A temporary voltage drop of the submodule battery in the
standby state, e.g. caused by storage below 0
o
C or a battery
change, is not detected by the battery monitor if the voltage dip is
corrected by plugging in the RAM submodule and switching on
the PLC. However, the voltage dip may have led to a loss or
corruption of RAM submodule data.
5
377 Memory Submodules
System Manual
C79000-B8576-C199-03
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