Siemens Simatic S7-1500 - Page 19

Hardware section
2.2 Installing the assembly
S7-1500
Getting Started, 05/2014, A5E03981761-AC
19
6. Insert the U-connector into the back of the digital input module.
7. Attach the digital input module to the mounting rail and screw tight.
8. Attach the digital output module to the mounting rail and screw tight.
Result
The assembly has been mounted.