What do the different terms and functions mean on DCC?

Hornby DCC Elite Train Controlller

Many of you will by now have seen or bought Hornby DCC (Digital) locomotives, controllers, decoders or accessories – but what do the terms and functions actually mean?  We’ve compiled a list of the most common terms with our colleagues at Hornby’s Technical Services team…

Acceleration Delay

The delay between the locomotive being stationary and reaching the desired speed.


Deceleration Delay

The delay of a locomotive slowing down to a standstill.


Accessory Decoder

An electronic decoder designed for use with track side accessories such as points or signals.An accessory decoder is not for use in a locomotive.



A number used to identify a locomotive or accessory that is either equipped or linked to a Decoder.


Feedback (Load Compensating)

This allows a locomotive to remain at a constant speed regardless of loads being pulled or incline being negotiated.



Technical term for wires that carry electrical signals around a model layout.


Command Station

The Command Station is the ‘brains’ of a DCC system.  A Command Station is in essence a micro-computer/controller that communicates with the decoders that are located either in a locomotive or connected accessory.  The computer transmits signals to the decoders instructing them what to do, such as accelerate, decelerate, brake or switch lights on or off.


Configuration Variable (CV)

A technical term referring to the operating information of the particular locomotive or accessory that is stored on the specific decoder.This information will remain “set” until changed using the Command Station.



Consist is an American term, but in the UK it is known by Double or Triple Heading.  This is where two or more locomotives are brought together and function as one.  There are three types of Consisting;

  1. Basic consisting where the locomotive decoders in the Consist have the same address.
  2. Universal Consisting where the Consist information is stored in the Command Station.
  3. Advanced Consisting is where the Consist information is stored inside the decoder.



Digital Command Control.  The application of computer technology to control the movements of locomotives.  Each locomotive is fitted with a decoder (or ‘chip’) which is uniquely programmed and recognises its own identity and responds only to those control signals which are addressed to it.  DCC also allows a wide range of extras including controllable lighting and on-board sound.  The accepted standards have been laid down by the NMRA (National Model Railroad Association) an American Association.


Locomotive Decoder

A small PC board which contains a ‘chip’ that stores control information; normally fitted in locomotives.  The Command Station sends coded information to the decoder which can then control the locomotives speed, direction and any operating functions that the locomotive may have e.g lights.  Locomotive Decoders can be fitted to accessories that have a motor as a drive for example the R070 Hornby Turntable.


Occupancy Decoder

A unit that can detect the presence of a locomotive on a specific section of track and can provide the appropriate information as ‘return’ data.


Power Bus

Copper strip or wires that can relay power from a Power Booster to the track.


Power Booster/Power Station

A Power Booster or Power Station is as the name implies, there to provide a boost of power to the track.  This can occur if a larger than normal quantity of locomotives are required to be running on the track at the same time.  If the transformer already fitted cannot handle this number then it will be necessary to section the layout and fit a Power Booster.  This Booster will not only provide more ampage to drive the locomotives but also boost the signals to the Decoders.  All Boosters fitted must still be connected to the Power Station.



The process of assigning an Address to a locomotive or accessory (points or signals).  The process of programming sends a signal containing a numerical identifier to the locomotive being programmed.


Programming Track

A section of track isolated from the main layout purposely for programming locomotives.  A Programming Track negates the requirement of removing other locomotives from the main layout.


Speed Steps

A variable voltage increase used to control motor speeds.  Decoders can set the output power for each speed step.


Stall Current

Stall Current is the maximum current draw in amperes that a locomotive is capable of when stalled.  If the armature of a motor is prevented from turning and the maximum voltage is applied the current draw of the motor is known as the “Stall Current”.


Throttle Notches

Determines whether a locomotive is controlled with 8, 14, or 18 speed steps.



A high-speed communication protocol used for connecting Digital input devices together.


XpressNet (XBUS) Input Devices

Devices using the XpressNet protocol to control a digital layout.