# Version check by FBs

The implementation of version monitoring by FB is based on the principle that each component of the ISG-MCP checks the version of the interfaces and PLC libraries it depends on itself. This is why some FB are implemented in the HLI library and in the motion library. These check the components or they return the version of the library

Generally, the user does not need to bother about this check because it is already done during startup of the PLC application by the instances of the MCV_Axis FB. These MCV_Axis instances are instanced in the MCV_P1_PLATFORM program which is invoked cyclically.

If inconsistencies occur, the other FB instances of the application are informed of them and they indicate FALSE at their "error" output and a specific error code at the the "error_id" output