Siemens SIMATIC ET 200S Installation And Operating Manual page 145

Wiring Diagram
Each of the four fail-safe digital outputs consists of a DOx P P-switch and a DOx M M-switch.
They connect the load between P and M-switches. The two switches are always controlled
so that voltage is applied to the load.
The wiring is carried out on an appropriate terminal module.
Figure 7-37
ET 200S Distributed I/O System - Fail-Safe Modules
Hardware Installation and Operating Manual, 07/2005, A5E00103686-04
7.6 4 F-DO DC24V/2A PROFIsafe digital electronic module
Wiring diagram of the EM 4 F-DO DC24V/2A PROFIsafe
Fail-Safe Modules
7-85