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Basic Principles – How Does It Work?

Posted by on Dec 18, 2014 in Miscellaneous, Tony's Tips |


With Digital Command Control (DCC) you use a handheld throttle to send information to a command station telling it what you want train X to do. The command station then takes this information, transforms it into a stream of digital packets and sends it to the booster. The booster will add power to the packets, and broadcast the combined signal to the rails.

  • DCC system sends commands
  • Loco decoders receive and act


The decoder-equipped locomotives on the railroad constantly listen to the ‘packet’ broadcast. Each information packet has an address component to it which should match the address of one of the decoders.

The decoder which is not the intended recipient of the packet simply ignores the data and its locomotive keeps on doing whatever it is doing – running forward, backward, lights on etc.

The decoder, to which the data packet IS addressed, will translate the packet into command for the locomotive such as ‘slow down’, ‘stop’, ‘reverse direction’, and the locomotive will behave accordingly.


  • The power on the tracks is alternating current (AC), and not DC or direct current.
  • Full power is running through the tracks at all times while the system is turned on. Voltage is sent by pulses to a decoder in a locomotive which controls the locomotive’s speed.
  • The polarity of electricity on the rail does not control locomotive direction. The decoder in each locomotive converts AC current to DC and controls the voltage and polarity that travel through the electric motor. When the decoder receives the digital signal sent from the command station, the decoder applies the appropriate amount of voltage and polarity to the motor based on the speed and direction in which you want the locomotive to travel.

Adapted from “DCC Made Easy”, by Lionel Strang, with permission of Kalmbach Publishing Co., and “DCC for Novices” by Stefano Curtarolo.