Siemens Simatic S7-1500 - Page 28

Hardware section
2.3 Wiring
S7-1500
28 Getting Started, 05/2014, A5E03981761-AC
3. Connect the four potential circuit bridges.
4. Connect the terminals 30 and 40, as well as 29 and 39 to each other.
Result
The digital output module is now wired.