Digital Command Control (DCC)

Advances in Model Railroading

Model railroad layout with fire engines
pejft / Getty Images

Digital Command Control (DCC) is an exciting field in model railroading that uses digital computer technology to operate model railroad trains.

  • 01 of 11

    What It Does

    The New Castle switch crew grabs CBRY 2125 and puts it on a track bound for Alliquippa where the car can be loaded. This short empty haul minimizes costs to the railroad.

    The Spruce / Ryan C Kunkle

    The DCC puts digital control information into the electrical power of the train. It can be referred to as the DCC signal, although it is both power and control information. The DCC signal is put on the model railroad's tracks.

    Then DCC mobile decoders in locomotives on the tracks use the DCC signal to power and control their locomotive's speed, direction, and lights. "Stationary decoders" may also be connected to operate the track's turnouts and other accessories.

  • 02 of 11

    How It Works

    dcc complete

    The Spruce / Ryan C Kunkle

    The user operates a throttle or cab equipped with a numeric keypad and other control buttons. Information from the throttle is sent to a DCC command station which converts it into DCC control information. This DCC control information is then fed to a booster which uses it to create the DCC signal and feed it to the tracks.

  • 03 of 11

    Why It's Modular

    The Rio Grande has come to life with the installation of the DCC control system.

    The Spruce / Ryan C Kunkle

    The throttle, command station, and booster may be individual electronic components or bundled in multi-function units. DCC's modular design makes it extremely flexible. Large layouts with lots of locomotives will require more power than one single booster can deliver, and every engineer will want his or her own throttle. DCC accommodates these requirements. Its modular design lets model railroaders tailor their DCC system to their own specific needs.

    Basic DCC starter systems are all-in-one units. If you're buying an all-in-one, make sure that it is expandable or can be integrated with the manufacturer's other, modular components.

  • 04 of 11

    Who Makes It

    NCE Powercab

    The Spruce / Ryan C Kunkle

    There are a number of manufacturers of DCC including Digitrax, Inc., Lenz Elektronik, GmbH, NCE Corporation, and Model Rectifier Corp. (MRC). Some sound manufacturers are​ Digitrax SoundFX and​ ESU Loksound.

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  • 05 of 11


    Decoder Installation

    The Spruce / Ryan C Kunkle

    The DCC standards specify voltage levels, pulse durations, and digital information formats. This means that a decoder from any manufacturer will respond to commands and programming signals from DCC systems made by any other manufacturer.

    The connection of DCC control system components has been left up to the individual manufacturers. Unfortunately, this means that throttles, command stations, and boosters from different manufacturers aren't usually compatible.

  • 06 of 11


    Packaged decoder

    The Spruce / Ryan C Kunkle

    Some manufacturers offer sound decoders. In addition to implementing all the standard DCC locomotive control functions, these decoders are connected to a small audio speaker through which they play locomotive sounds. Diesel locomotives play a diesel motor hum which changes pitch relative to engine speed. Steam locomotives emit the characteristic chuff sounds at speed appropriate rates. Brakes squeal and valves hiss. High-end sound decoders feature programmable sound tables. Using a computer equipped with proprietary sound decoder programming software and interfaced with the DCC controller, users of high-end sound decoders may customize the sounds played by their locomotives.

  • 07 of 11

    Control Execution

    This NCE decoder is installed on an Athearn HO locomotive frame and motor.

    The Spruce / Ryan C Kunkle

    Each locomotive on the track layout is equipped with a uniquely addressed DCC mobile decoder. Using a throttle, the operator can select any locomotive on the track by its address and alter its speed, direction, lighting, and other features. DCC allows multiple throttles to control different locomotives simultaneously. Unselected locomotives continue running at their last settings. The brand and model of a particular command station determines how many locomotives may be run simultaneously on your layout.

    The DCC decoder has a power circuit that converts the DCC power signal into DC power for the motor and lights. The decoder also has digital logic which uses the power signal information to control the locomotive.

  • 08 of 11

    Decoder Programming

    switch decoder program

    The Spruce / Ryan C Kunkle

    Decoder programming has evolved a bit since the introduction of DCC. Originally locomotives could only be programmed on a programming track. DCC controllers have special terminals for connecting a programming track. The locomotive cannot run on the programming track; it can only be programmed there.

    Decoders are configured by setting configuration variables, or CVs. Today some decoders allow CV values to be programmed while the train is running on the main track. The one exception is that the CV values specifying the locomotive's unique address cannot be changed while running. Addresses can only be changed on the programming track.

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  • 09 of 11

    Decoder Addressing


    The Spruce / Ryan C Kunkle

    Most decoders are shipped with their locomotive addresses set to 3. Each locomotive on a layout must have a unique address, so new DCC equipped locomotives and those that have just had decoders installed need their addresses reprogrammed. Many modelers program a locomotive's address to the locomotive's road number or the number painted on the locomotive itself.

    Programming addresses can only be done when the locomotive is on a programming track. This is because the programming signal would change the addresses of all locomotives on your track if you didn't isolate the locomotive you want to program on the programming track.

  • 10 of 11

    Reading Decoder Configuration Variable (CV) Values

    Early decoders could only be written to. When a CV was programmed with a new value, the decoder could only respond by flashing the lights and pulsing the motor of the locomotive to indicate that it had received the update. Most decoders still flash lights and pulse motors, but newer decoders can transmit CV values back to the DCC command station through the tracks, though not all command stations and throttles can receive and display them.

  • 11 of 11

    Standards Organizations

    Current DCC standards have been adopted by both the National Model Railroad Association (NMRA) and the European Union of Model Railroad and Railroad Friends (MOROP).