The CDV-BDU is a bus controller for 2EASY 2-Wire video entry systems and can be used in three different modes: amplifier, system expander, or gateway. Amplifier mode increases maximum cable distance. System expander mode facilitates multiway systems up to 128 users. Gateway mode allows a main door panel to be added in a multi-block complex. The main door panel can call all apartments, instead of only those in the associated block.