Siemens S5-135U/155U appendix Function of the Enable Inputs, With an Active

Digital Input/Output Modules

8.1.2Function 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:

SThe module can no longer be addressed by the user program.

SAll 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.

With an Active	On digital input/output modules with DC voltage inputs or outputs, the
Enable Input	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

System Manual	8-5
C79000-G8576-C199-06