Siemens SINAMICS Series Function Manual page 71

5.3 Control of "STO" and "SS1" via terminals on the Control Unit and the Motor/Power Module
Note
An open input is interpreted as "low".
To enable the digital inputs (DI) to function, terminal M1 must be connected.
This is achieved by:
1. Providing the ground reference of the digital inputs, or
2. A jumper to terminal M.
This removes isolation for these digital inputs.
Note
If the 24 V supply is briefly interrupted, the digital outputs are deactivated for this time.
Safety Integrated
Function Manual, 07/2016, A5E03264275A
Controlling the safety functions
71