Siemens SIMATIC ET 200SP System Manual page 118

Plugging in I/O modules and BU covers
Watch video sequence: "Insert I/O modules"
(http://support.automation.siemens.com/WW/view/en/95886218)
Insert the I/O module or BU cover parallel into the BaseUnit until you hear both latches click
into place.
Figure 6-14
Distributed I/O system
System Manual, 09/2019, A5E03576849-AJ
6.13 Inserting I/O modules / motor starters and BU covers
Plugging in I/O modules or BU covers (using an I/O module as example)
Wiring
117