FAQ:What are the NMRA Digital Command Control Standards?
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In the late 1980s, the National Model Railroad Association (NMRA) began investigating a standard for command control systems. All the analog based command control systems available on the market had limitations which inhibited expansion, and they were never compatible amongst themselves. The NMRA's command control committee decided that digital was the way to go, and the best way was to use a 100% digital signal on the track.
What caught their attention were the digital systems used in Europe, originating mainly from Germany. One system in particular was promoted by Marklin. The NMRA would examine two digitally based command control systems, from Marklin and Keller Engineering. After examining the commercial offerings, a standard emerged, the Digital Command Control System.
In doing so, it created a basic standard which is compatible across most Digital Command Control manufacturers. This allows us to use a brand XYZ decoder which is controlled by brand ABC DCC system.
Compatibility of Digital Command Control components is defined at the track level. This allows decoders from different manufacturers to work together, but permits manufacturers to innovate on the user interface, throttle, and command station capabilities. Certain parameters of the decoder are defined by the NMRA, but the designers and manufacturers may add additional features (such as sound), providing they do not impair the basic decoder operations.
The complete (and rather technical) NMRA DCC Standards can be found on the NMRA web site.