Siemens S5-135U/155U - Manual (Page 226)

5-86
System Manual
C79000-G8576-C199-06
In this standby state of the unit
S
the battery-backed RAM submodule is in the CPU;
S
the PLC is switched off (Power Off);
S
the backup battery of the PLC is providing backup of the RAM
submodule;
S
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.
In this standby state of the submodule
S
the RAM submodule has been removed from the CPU;
S
the submodule battery is providing backup of the RAM submodule;
S
the contents of the battery-backed RAM are retained.
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:
S
Submodule battery is not present.
S
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.
Standby Operation
Submodule
Standby
Battery Monitoring
and Battery Fault
CPUs, Memory Cards, Memory Submodules, Interface Submodules