What is DCC?


By Howard Smith

20 March 2020

DCC or Digital Command Control is a system of model railway operation which uses digital signals to control locomotives and accessories.

Digital Command Control (often shortened to DCC) is now the most popular method of controlling a model railway. It offers advantages in model railway operation by allowing a locomotive to be controlled wherever it is on a section of a model railway, without controlling another locomotive, even if both are on the same section of track. Just prior to DCC control, DC control was the most popular method of model railway operation, though it requires more wires and switches than a DCC layout.

The DCC system was pioneered by Lenz GmbH of Germany for two German model railway manufacturers. The first decoders appeared on the market in 1989 for Arnold and 1990 for Märklin. The DCC protocol is defined by the Digital Command Control Working group of the National Model Railroad Association (NMRA) and is updated accordingly.

Hornby R8213 DCC controller

Hornby's entry level (R8213) Select DCC Controller.

A DCC system traditionally operates using a command station in combination with its power supply and decoders. The command station sends signals of command and receives signals or feedback from certain types of decoders, or when these decoders are interrogated using the command station. The command station 'controls' the model railway system. It sends a series of signals over a permanent current through wires which are referred to as 'bus wires'.

Hornby R8245 decoder

Hornby's R8245 DCC decoder

The signals from the command station are received by decoders which are fitted inside locomotives, accessories or any item of rolling stock, so long as these are connected permanently in some way to the bus wires. Locomotive decoders use the same pick ups fitted to wheels which are in contact with the track, hence permanently receive signals from the command station. Decoders make sense of the signals emitted by a command station and in turn operate either the motor of the locomotive or its accessories, lights or sounds (if fitted). All decoders receive the signals, though through an address system (similar to a post system), only the decoder with the correct address will act upon the signals received.