Siemens SIMATIC S7-1500 System Manual page 185

Coding element in the front connector
When the front connector is inserted into the I/O module for the first time, one half of the
coding element latches into the front connector. When you remove the front connector from
the I/O module, this half of the coding element remains in the front connector, while the other
half remains in the I/O module.
Figure 13-2 Coding element in the I/O module/front connector
You can insert a coded front connector on modules with the same electrical pin assignment.
Please note the Application Planning (Page 23) section.
NOTICE
Physical damage can occur
If the coding element is changed or removed, it will be possible to insert the front connector
on modules in which the electrical connection is not properly wired.
This can destroy the module and/or the connected sensors and actuators. Even hazardous
plant states are possible.
Do not change the coding element unless you want to use the front connector on a different
module and you change the process wiring accordingly.
Use cases for replacing the coding element
● Replacing an I/O module, for example, due to a defect or incorrect configuration
● Replacing a front connector
Automation system
System Manual, 12/2014, A5E03461182-AC
13.2 Replacement of I/O modules and front connectors
Maintenance
185