# Bidirectional congruence checking of the HLI memory interface

The ISG FBs send commands to the ISG-MCE via the so-called HLI. As this is a memory-coupled interface, congruent post-definition of this interface in the PLC is the prerequisite for correct functioning of the overall system. This is why a congruence check is realised in the MCP library to ensure that the HLI interface is not operated with an incorrect HLI emulation.