Siemens S5-135U/155U System Manual page 318

Digital Input/Output Modules
Jumper inserted:
Jumper open:
With Enable Input
If removal and insertion of modules during operation is not required, you
Switched Off
must remove the plug-in jumper for changeover of the enable mode. Wiring
of the enable inputs (F+/F-) can then be dispensed with.
Examples of Almost power-free shutdown of individual subprocesses, i.e. outputs of
Functioning of the various modules can be operated from a common load supply and yet
Enable Inputs
activated separately.
The load voltage of each individual module can be monitored without
additional circuitry. Any reactions to failure of the load voltage can be
programmed in the QVZ (timeout) organization block.
You must observe the following when configuring systems:
Switching on
Switching off
You should observe the following instructions for switching off PLCs and
equipment for supplying power to the enable inputs:
24 V supply for CC/EU and I/Os
Enable supply from:
a) Battery
b) Terminals for 24 V on the front plate of the power supply
8-6
Enable input (F+/F-) active (factory setting)
Enable input (F+/F-) switched off
At the latest 100 ms after power-up of the PLC, the voltage must be
present at the enable inputs of the I/O modules.
When the PLC has been switched off, the voltage at the enable in-
puts of the I/O modules must still be present as long as voltage is
applied to the CC/EU.
CC/EU
24V Power Supply
24 V DC
a)
Battery
b)
I/O Modules
F+
L+
L+
System Manual
C79000-G8576-C199-06