Digital Command Control (DCC) is a scheme for controlling locomotives on a model railroad layout that allows more than one locomotive to occupy the same electrical section of track. Each of the locomotives has a decoder between the track and the motor, an electronic circuit that reads messages sent over the track and controls the amount of electricity delivered to the motor. A command station/booster places both the power and the messages on the track using a scheme where the actual power modulation encodes the digital bits of the messages.
The key advantage of using DCC is the elimination of electrically isolated blocks of track to allow the operation of multiple locomotives on the same layout.
The DCC protocol is the subject of two standards published by the National Model Railroad Association: S-9.1 specifies the electrical standard, and S-9.2 specifies the communications standard. The standards, along with recommended practice documents and other information, can be found at the NMRA DCC Standards and Recommanded Practices Page.
