Siemens Simatic S7-1500 - Page 26

Hardware section
2.3 Wiring
S7-1500
26 Getting Started, 05/2014, A5E03981761-AC
2. Thread in the cable tie.
3. Connect the supply voltage 24 V DC to the terminals 20 (M) and 19 (L+).
4. Insert the potential circuit bridges between the two bottom terminals.
Result
The digital input module is now wired.