Siemens S5-135U/155U System Manual page 226

CPUs, Memory Cards, Memory Submodules, Interface Submodules
Standby Operation
In this standby state of the unit
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 In this standby state of the submodule
Standby
Battery Monitoring
The battery of the battery-backed RAM submodule is monitored. When the
and Battery Fault
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:
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
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.
5-86
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.
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.
Submodule battery is not present.
Submodule battery is faulty (voltage less than 2.6 V).
o
C or a battery change, is not detected by the
System Manual
C79000-G8576-C199-06