Siemens S5-135U/155U appendix Standby Operation

CPUs, Memory Cards, Memory Submodules, Interface Submodules

Standby Operation	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.
Submodule	In this standby state of the submodule
Standby	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.

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:

SSubmodule battery is not present.

SSubmodule 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 oC 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.

5-86	System Manual
	C79000-G8576-C199-06