Editing Digital Command Control (section)

==History==
A digital command control system was developed (under contract by Lenz Elektronik GmbH of Germany) in the 1980s for two German model railway manufacturers, [[Märklin]] and [[Arnold (models)|Arnold]]. The first digital decoders that Lenz produced appeared on the market early 1989 for Arnold ([[N scale]]) and mid 1990 for Märklin ([[Z scale]], [[HO scale|H0 scale]] and [[1 gauge]]; Digital=).<ref>Werner Kraus. (1991). ''Modellbahn Digital Praxis: Aufbau, Betrieb und Selbstbau.'' Düsseldorf: Alba. {{ISBN|3-87094-567-2}}</ref> Märklin and Arnold exited the agreement over patent issues, but Lenz continued to develop the system. In 1992 Stan Ames, who later chaired the NMRA/DCC Working Group, investigated the Märklin/Lenz system as possible candidate for the NMRA/DCC standards. When the NMRA Command Control committee requested submissions from manufacturers for its proposed command control standard in the 1990s, Märklin and [[Keller Engineering]] submitted their systems for evaluation.<ref>DCC Home Page [http://www.nmra.org/dcc-rps-standards "DCC Home Page"], ''NMRA.org'', accessed December 19, 2010.</ref> The committee was impressed by the Märklin/Lenz system and had settled on digital early in the process. The NMRA eventually developed their own protocol based on the Lenz system and further extended it. The system was later named Digital Command Control. The first commercial systems built on the NMRA DCC were demonstrated at the 1993 NMRA Convention, when the proposed DCC Standard was announced. The proposed standard was published in the October 1993 issue of ''Model Railroader'' magazine prior to its adoption.
 
The DCC protocol is the subject of two [[standardization|standards]] published by the NMRA: S-9.1 specifies the electrical standard, and S-9.2 specifies the [[communications protocol|communications]] standard. Several recommended practices documents are also available.

The DCC protocol defines signal levels and timings on the track. DCC does not specify the protocol used between the DCC command station and other components such as additional throttles. A variety of proprietary standards exist, and in general, command stations from one vendor are not compatible with throttles from another vendor.

=== RailCom ===
In 2006 Lenz, together with Kühn, Zimo and Tams, started development of an extension to the DCC protocol to allow a feedback channel from decoders to the command station. This feedback channel can typically be used to signal which train occupies a certain section, but as well to inform the command station of the actual speed of an engine. This feedback channel is known under the name RailCom,<ref>{{Cite web |date=2023-10-30 |title=Digital Command Control and RailCom |url=https://dccwiki.com/RailCom |access-date=2023-11-16 |website=DCCWiki |language=en}}</ref> and was standardized in 2007 as NMRA RP 9.3.1.

Quoting "NMRA Standards and Recommended Practices":<ref name="NMRA Standards and Recommended Practices">DCC Home Page [https://www.nmra.org/index-nmra-standards-and-recommended-practices "S-9.3.1 (discontinued)"], ''NMRA.org'', accessed November 23, 2018.</ref>

:S-9.3 DCC Bi-Directional Communications Standard
::S-9.3.1 (discontinued)
::S-9.3.2 DCC Basic Decoder Transmission - (updated 12/20/2012) UNDER REVISION