Siemens S5-135U/155U RAM Submodules with Battery Backup, Operational States, Normal Operation

CPUs, Memory Cards, Memory Submodules, Interface Submodules

5.10.3RAM Submodules with Battery Backup

	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.
Operational States	There are three different operational states for the RAM submodule with
	battery backup:
Normal Operation	In this state
	S the battery-backed RAM submodule is in the CPU;
	S the programmable controller (PLC) is switched on (Power On);
	S 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	5-85
C79000-G8576-C199-06