Siemens SINAMICS S120 Device Manual page 429

Note
Ensuring the function of digital inputs
An open input is interpreted as "low".
To enable the digital inputs (DI) to function, terminal M1 must be connected.
This is achieved through one of the following measures:
1. Provision of the ground reference of the digital inputs.
2. A jumper to terminal M (Note the following: This removes the electrical isolation for these
digital inputs.)
Note
If the 24 V supply is briefly interrupted, then the digital outputs are deactivated during this
time.
Cabinet Modules NEMA
Manual, 04/2014, A5E03586450A
8.22 K95, CU320-2 PN Control Unit
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