• Guide to DCC
• Potted History
• The NMRA Standard
• How It Works
• The Advantages
• What DCC Cannot Do
• The Numbers Game
• Wiring the Layout

How It Works

Short Summary

With Digital Command Control (DCC) you use a controller (also called cabs or throttles) 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 code and sends it to the booster. The booster will add power to the code, and broadcast the combined signal to the rails and hence to the decoders. In most modern systems the basic set combines the command and booster functions in a single unit; the NCE Power Pro and Gaugemaster systems are typical examples.

DCC systems send commands and decoders receive and act on them

Packet Broadcast

The digital instructions are sent out in 'packets' all of which comprise three elements:

• An address component
• An instruction
• A quality control element which confirms that the message is correct.

The decoder-equipped locomotives or accessories on the railway 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.  Any decoder which is not the intended recipient of the packet simply ignores the data  and its locomotive keeps on doing whatever it was last told to do -  running forward, backward, lights on etc.

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

The power on the tracks is a form of alternating current (AC), and not DC or direct current.  Full power is running through the tracks at all times while 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.

The digital code is included in the power by varying (modulating) the AC waveform which runs at a much higher frequency than domestic electricity supplies.  All of the power is also the message which greatly enhances the effectiveness of transmission.