The MCX4D is an I/O expander designed to work in the RACS 5 access control system. The module is dedicated to support 4 doors, distributes power supply and communication bus to controlled doors, and supports a backup battery.

For each controlled door it provides: 2 signal inputs, 2 control outputs, communication interface to readers and 2 supply outputs. The door circuits are electrically separated what assures that in case of malfunction or sabotage, the problem which occurred on a single door is not propagated to other doors. The MCX4D expander is supplied from the external 13.8 VDC power supply which provides energy for the entire door control system including door locks and readers. In case of main supply failure, entire system is supplied from the reserve battery which can be charged depending on the needs.