Siemens S5-135U/155U - Manual (Page 317)

8-5
System Manual
C79000-G8576-C199-06
8.1.2 Function of the Enable Inputs
The digital input/output modules have an enable circuit. You can use the
enable inputs to implement electrical interlocks for certain modules or switch
off individual modules, whilst the PLC is in operation.
This means that:
S
The module can no longer be addressed by the user program.
S
All outputs of digital output modules are set to zero.
Modules which are switched off can be removed or inserted during operation.
If this is not necessary, operate the module with the enable input switched
off.
On digital input/output modules with DC voltage inputs or outputs, the
enable circuit requires that enable inputs F+ and F- be wired in the front
connector. Enabling is achieved by applying an external voltage to inputs
F+/F-. Modules for AC voltage have a wire jumper in the front connector.
When the front connector is swivelled away from the front strip of the
module, the supply of power to the enable input is interrupted, i.e. the wire
jumper in the front connector is removed; the module is switched off and can
no longer be addressed by the user program.
When the front connector is swivelled away, i.e. the voltage is removed from
the enable inputs, a timeout (QVZ) occurs at the CPU (see the Programming
Guide for the particular CPU).
Apart from the 6ES5 458-4UC11 digital output module, all digital
input/output modules additionally offer the facility for changing the enable
mode. The modules have a jumper accessible from above in the vicinity of
the addressing switch (see Figure 8-2).
Enable Jumper
Figure 8-2 Location of the Enable Jumper
With an Active
Enable Input
Digital Input/Output Modules