Digital Command Control: Difference between revisions
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{{Short description|System for digital control of model railways}} |
{{Short description|System for digital control of model railways}} |
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{{More citations needed |date=April 2024}} |
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{{Other uses|DCC (disambiguation)}} |
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'''Digital Command Control''' (DCC) is a standard for a system for the digital operation of [[model railways]] that permits locomotives on the same electrical section of track to be independently controlled. |
'''Digital Command Control''' (DCC) is a standard for a system for the digital operation of [[model railways]] that permits locomotives on the same electrical section of track to be independently controlled. |
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The DCC protocol is defined by the Digital Command Control Working group of the US [[National Model Railroad Association]] (NMRA). The NMRA has trademarked the term DCC{{Citation needed|reason=Only the DCC compatibility logo was trademarked, TESS Registration Number 77103259|date=May 2021}}, so while the term ''Digital Command Control'' is sometimes used to describe any digital model railway control system, strictly speaking it refers to NMRA DCC. |
The DCC protocol is defined by the Digital Command Control Working group of the US [[National Model Railroad Association]] (NMRA). The NMRA has trademarked the term DCC{{Citation needed|reason=Only the DCC compatibility logo was trademarked, TESS Registration Number 77103259|date=May 2021}}, so while the term ''Digital Command Control'' is sometimes used to describe any digital model railway control system, strictly speaking it refers to NMRA DCC. |
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==History |
==History== |
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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. |
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. |
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::S-9.3.2 DCC Basic Decoder Transmission - (updated 12/20/2012) UNDER REVISION |
::S-9.3.2 DCC Basic Decoder Transmission - (updated 12/20/2012) UNDER REVISION |
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== |
==Function== |
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[[File:DCCsig.png|thumb|right|A |
[[File:DCCsig.png|thumb|right|A sequence of 7 bits encoded with DCC. Note the peak-to-peak voltage is constant and thus does not carry information. Note the given values of time are for each half-cycle of a square wave.]] |
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A basic DCC system consists of a command station, power stations, throttles and decoders. Any DCC system will only have one command station. The command station acts as an interface between the throttles and the decoders. Power stations (commonly known as boosters), which act as current [[Amplifier|amplifiers]], provide most, or all, of the electrical power required by the DCC vehicles. The number of power stations depend on the number of vehicles that are intended to receive commands (and thus draw current) from any one command station. Throttles, both virtual and physical, provide an interface for the user to interact with the DCC system. Commands issued by the user via a throttle are sent to the command station to be forwarded to the decoders. Typically a user will operate one or two throttles at a given time. Decoders are receivers to commands forwarded from the command station. Each decoder is assigned an address and respond only to commands issued to their respective address, hence it can be thought that they 'decode' messages. Some decoders are [[Transceiver|transceivers]], which can transmit data back to the command station to be forwarded to the throttles. Mobile decoders are designed to be installed in a moving vehicle, such as a locomotive, and control nearly every aspect of the vehicle's behaviour, such as direction of travel, speed of travel, lighting effects and sound effects. Accessory or stationary decoders enable basic [[General-purpose input/output|GPIO]] to operate any other stationary features, such as [[Railroad switch|turnouts]], [[Railway signal|signals]], or any animated scenes. |
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A DCC system consists of power supplies, command stations, boosters, throttles and decoders. |
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The DCC command station creates the digital packet using data from a throttle. The digital packet contains the decoder's address, instructions and an error byte to check the validity of the packet. |
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The electrical waveform sent to the decoders (typically along the model railway track) serves as both a digital signal and carrier of electric [[Power (physics)|power]]. The power carried is the [[Amplitude|peak-to-peak]] voltage multiplied by the current. The voltage is specified by the NMRA to be based on the [[Rail transport modelling scales|modelling scale]]. The data is encoded via [[frequency modulation]] by varying the period of individual [[Square wave|square waves]]. A [[binary numeral system|binary]] 1 is represented by a {{val|116|ul=μs}} nominal period, while a 0 is represented by a {{val|200|u=μs}} nominal period. These 0 and 1 bits form packets which contain a preamble, the recipient decoder's address, an instruction, and a [[checksum]]. As such, the digital signal is encoded entirely in time and is completely independent of the waveform voltage. As there is no long-term polarity in the waveform, direction of travel of a DCC vehicle is independent of the [[Instant|instantaneous]] polarity between the rails, as it would in conventional DC operation. There is no ground reference in the DCC signal, and as such, either rail may be used as a reference. Additionally, this means that a square wave beginning with a [[Signal edge|rising edge]] is interpreted identically as a square wave beginning with a falling edge, as long as the period of the waves are the same. |
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Many command stations are integrated with an amplifier (booster) which, in combination with its power supply, [[modulation|modulates]] the voltage on the track to encode [[Digital data|digital]] messages while providing electric power. For large systems additional boosters may be employed to provide extra power. |
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The track voltage is a pure digital signal, described as a Differential Signal with no ground reference<ref>NMRA Standard S-9.1</ref>. One rail is always the inverse logical state of the other, with each data pulse repeated. The DCC signal does not follow a [[sine wave]], nor is it a carrier superimposed on a DC voltage. The command station/booster quickly switches the voltage applied to the rails on and off, resulting in a binary stream of pulses. As there is no polarity, direction of travel is independent of the rail's phase. The length of time the voltage is applied provides the method for encoding data. To represent a [[binary numeral system|binary]] one, the period is short (nominally 106 [[Microsecond|µs]]), while a zero is represented by a longer period (nominally at least 200 µs). |
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Each locomotive is equipped with an individually addressed multifunction [[Dcc:Decoder|DCC decoder]] that takes the signal from the track, processes and acts on the instructions. The [[electric motor]]'s speed and direction is controlled using [[Pulse-width modulation|Pulse Width Modulation]]. Each decoder is given a unique [[Address space|address]], and will not act on commands intended for a different decoder, thus providing independent control of locomotives and accessories anywhere on the layout without special wiring requirements. Decoders can also control functions such as lights, smoke generators, and sound generators. These functions can be operated remotely from the DCC throttle. [[Dcc:Stationary decoder|Accessory decoders]] can also receive commands from the throttle in a similar way to allow control of turnouts, uncouplers and other operating accessories (such as station announcements) and lights. |
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It is possible to power a single analog (DC) model locomotive by itself (or in addition to the DCC decoder equipped engines), depending on the choice of commercially available DCC starter systems. The technique is known as [[Dcc:zero stretching| zero stretching]] and is not part of the NMRA DCC Standard. The zero bit's period can be expanded (stretched) to make the average voltage (and thus the current) either forward or reverse, depending on which rail the stretched zero bit is applied to. However, because the raw power contains a large harmonic component, DC motors heat up much more quickly than they would on DC power, and some motor types (particularly [[Electric motor#Ironless or coreless rotor motor|coreless electric motors]]) can be damaged by a DCC signal. |
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==Advantages over analog control== |
==Advantages over analog control== |
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[[File:DCC decoder installed in an N scale LifeLike Berkshire Steam Locomotive.jpg|thumb|right|A DCC decoder installed in an {{nowrap|[[N scale]]}} steam locomotive]] |
[[File:DCC decoder installed in an N scale LifeLike Berkshire Steam Locomotive.jpg|thumb|right|A DCC decoder installed in an {{nowrap|[[N scale]]}} steam locomotive]] |
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The great advantage of digital control is the individual control of locomotives wherever they are on the layout. With analog control, operating more than one locomotive independently requires the track to be wired into separate |
The great advantage of digital control is the individual control of locomotives wherever they are on the layout. With analog control, operating more than one locomotive independently requires the track to be wired into separate blocks each having switches to select the controller. Using digital control, locomotives may be controlled wherever they are. |
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Digital locomotive decoders often include |
Digital locomotive decoders often include inertia simulation, where the locomotive will gradually increase or decrease speeds in a realistic manner. Many decoders will also constantly adjust motor power to [[Cruise control|maintain constant speed]]. Most digital controllers allow an operator to set the speed of one locomotive and then select another locomotive to control its speed while the previous locomotive maintains its speed. |
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Recent developments include on-board sound modules for locomotives as small as |
Recent{{When|date=February 2024}} developments include on-board sound modules for locomotives as small as N scale, made possible by advancements in [[smartphone]]s, which tend to use small yet high-quality speakers. |
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Wiring requirements are generally reduced compared to a conventional DC powered layout. With digital control of accessories, the wiring is distributed to accessory decoders rather than being individually connected to a central control panel. For portable layouts this can greatly reduce the number of inter-board connections - only the digital signal and any accessory power supplies need cross baseboard joins. |
Wiring requirements are generally reduced compared to a conventional DC powered layout. With digital control of accessories, the wiring is distributed to accessory decoders rather than being individually connected to a central control panel. For portable layouts this can greatly reduce the number of inter-board connections - only the digital signal and any accessory power supplies need cross baseboard joins. |
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== |
== Schematics == |
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[[File:Schema DCC en.svg|720px|DCC command]] |
[[File:Schema DCC en.svg|720px|DCC command]] |
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Other systems include the [[Digital model railway control systems|Digital Command System]] and [[Trainmaster Command Control]]. |
Other systems include the [[Digital model railway control systems|Digital Command System]] and [[Trainmaster Command Control]]. |
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Several major manufacturers (including Märklin, [[Fleischmann_(model_railroads)|Fleischmann]], [[Roco]], [[Hornby Railways|Hornby]] and [[Bachmann Industries|Bachmann]]), have entered the DCC market alongside makers which specialize in it (including Lenz, Digitrax, ESU, ZIMO, Kühn, Tams, NCE, Digikeijs, and CVP Products, Sound Traxx, Train Control Systems and ZTC). Most Selectrix central units are multi protocol units supporting DCC fully or partially (e.g. Rautenhaus, Stärz and MTTM). |
Several major manufacturers (including Märklin, [[Fleischmann_(model_railroads)|Fleischmann]], [[Roco (model railroads)|Roco]], [[Hornby Railways|Hornby]] and [[Bachmann Industries|Bachmann]]), have entered the DCC market alongside makers which specialize in it (including Lenz, Digitrax, ESU, ZIMO, Kühn, Tams, NCE, Digikeijs, and CVP Products, Sound Traxx, Train Control Systems and ZTC). Most Selectrix central units are multi protocol units supporting DCC fully or partially (e.g. Rautenhaus, Stärz and MTTM). |
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== See also == |
== See also == |
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* [[Digital model railway control systems]] |
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* [[List of network buses]] |
* [[List of network buses]] |
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==References== |
==References== |
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{{reflist}} |
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<references/> |
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==Further reading== |
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*{{cite magazine|title=Digital Command Control: a beginner's guide|magazine=Hornby Magazine|first=Mike|last=Wild|page=88–92|issue=1|date=April–May 2007|location=Hersham|publisher=Ian Allan Publishing|issn=1753-2469|oclc=226087101}} |
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*{{cite magazine|title=DCC: The Way Ahead|first=Phil|last=Grainger|magazine=[[Model Rail]]|pages=40–41|issue=113|date=January 2008|location=Peterborough|publisher=EMAP Active|issn=1369-5118|oclc=173324502}} |
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==External links== |
==External links== |
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*[http://dccwiki.com/ The DCCWiki] |
*[http://dccwiki.com/ The DCCWiki] |
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*[http://www.WiringForDCC.com/ Wiring for DCC] |
*[http://www.WiringForDCC.com/ Wiring for DCC] |
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*[https://dcc-ex.com DCC-EX - An open-source DCC centrale software] |
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*[http://www.opendcc.de/index_e.html/ OpenDCC - An open project for building your own decoders, command stations etc.] |
*[http://www.opendcc.de/index_e.html/ OpenDCC - An open project for building your own decoders, command stations etc.] |
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Latest revision as of 17:47, 4 December 2024
 | This article needs additional citations for verification. (April 2024) |
Digital Command Control (DCC) is a standard for a system for the digital operation of model railways that permits locomotives on the same electrical section of track to be independently controlled.
The DCC protocol is defined by the Digital Command Control Working group of the US National Model Railroad Association (NMRA). The NMRA has trademarked the term DCC[citation needed], so while the term Digital Command Control is sometimes used to describe any digital model railway control system, strictly speaking it refers to NMRA DCC.
History
[edit]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. The first digital decoders that Lenz produced appeared on the market early 1989 for Arnold (N scale) and mid 1990 for Märklin (Z scale, H0 scale and 1 gauge; Digital=).[1] 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.[2] 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 standards published by the NMRA: S-9.1 specifies the electrical standard, and S-9.2 specifies the 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
[edit]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,[3] and was standardized in 2007 as NMRA RP 9.3.1.
Quoting "NMRA Standards and Recommended Practices":[4]
- 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
Function
[edit]
A basic DCC system consists of a command station, power stations, throttles and decoders. Any DCC system will only have one command station. The command station acts as an interface between the throttles and the decoders. Power stations (commonly known as boosters), which act as current amplifiers, provide most, or all, of the electrical power required by the DCC vehicles. The number of power stations depend on the number of vehicles that are intended to receive commands (and thus draw current) from any one command station. Throttles, both virtual and physical, provide an interface for the user to interact with the DCC system. Commands issued by the user via a throttle are sent to the command station to be forwarded to the decoders. Typically a user will operate one or two throttles at a given time. Decoders are receivers to commands forwarded from the command station. Each decoder is assigned an address and respond only to commands issued to their respective address, hence it can be thought that they 'decode' messages. Some decoders are transceivers, which can transmit data back to the command station to be forwarded to the throttles. Mobile decoders are designed to be installed in a moving vehicle, such as a locomotive, and control nearly every aspect of the vehicle's behaviour, such as direction of travel, speed of travel, lighting effects and sound effects. Accessory or stationary decoders enable basic GPIO to operate any other stationary features, such as turnouts, signals, or any animated scenes.
The electrical waveform sent to the decoders (typically along the model railway track) serves as both a digital signal and carrier of electric power. The power carried is the peak-to-peak voltage multiplied by the current. The voltage is specified by the NMRA to be based on the modelling scale. The data is encoded via frequency modulation by varying the period of individual square waves. A binary 1 is represented by a 116 μs nominal period, while a 0 is represented by a 200 μs nominal period. These 0 and 1 bits form packets which contain a preamble, the recipient decoder's address, an instruction, and a checksum. As such, the digital signal is encoded entirely in time and is completely independent of the waveform voltage. As there is no long-term polarity in the waveform, direction of travel of a DCC vehicle is independent of the instantaneous polarity between the rails, as it would in conventional DC operation. There is no ground reference in the DCC signal, and as such, either rail may be used as a reference. Additionally, this means that a square wave beginning with a rising edge is interpreted identically as a square wave beginning with a falling edge, as long as the period of the waves are the same.
Advantages over analog control
[edit]
The great advantage of digital control is the individual control of locomotives wherever they are on the layout. With analog control, operating more than one locomotive independently requires the track to be wired into separate blocks each having switches to select the controller. Using digital control, locomotives may be controlled wherever they are.
Digital locomotive decoders often include inertia simulation, where the locomotive will gradually increase or decrease speeds in a realistic manner. Many decoders will also constantly adjust motor power to maintain constant speed. Most digital controllers allow an operator to set the speed of one locomotive and then select another locomotive to control its speed while the previous locomotive maintains its speed.
Recent[when?] developments include on-board sound modules for locomotives as small as N scale, made possible by advancements in smartphones, which tend to use small yet high-quality speakers.
Wiring requirements are generally reduced compared to a conventional DC powered layout. With digital control of accessories, the wiring is distributed to accessory decoders rather than being individually connected to a central control panel. For portable layouts this can greatly reduce the number of inter-board connections - only the digital signal and any accessory power supplies need cross baseboard joins.
Schematics
[edit]
Competing systems
[edit]There are two main European alternatives: Selectrix, an open Normen Europäischer Modellbahnen (NEM) standard, and the Märklin Digital proprietary system. The US Rail-Lynx system provides power with a fixed voltage to the rails while commands are sent digitally using infrared light.
Other systems include the Digital Command System and Trainmaster Command Control.
Several major manufacturers (including Märklin, Fleischmann, Roco, Hornby and Bachmann), have entered the DCC market alongside makers which specialize in it (including Lenz, Digitrax, ESU, ZIMO, Kühn, Tams, NCE, Digikeijs, and CVP Products, Sound Traxx, Train Control Systems and ZTC). Most Selectrix central units are multi protocol units supporting DCC fully or partially (e.g. Rautenhaus, Stärz and MTTM).
See also
[edit]References
[edit]- ^ Werner Kraus. (1991). Modellbahn Digital Praxis: Aufbau, Betrieb und Selbstbau. Düsseldorf: Alba. ISBN 3-87094-567-2
- ^ DCC Home Page "DCC Home Page", NMRA.org, accessed December 19, 2010.
- ^ "Digital Command Control and RailCom". DCCWiki. 2023-10-30. Retrieved 2023-11-16.
- ^ DCC Home Page "S-9.3.1 (discontinued)", NMRA.org, accessed November 23, 2018.
Further reading
[edit]- Wild, Mike (April–May 2007). "Digital Command Control: a beginner's guide". Hornby Magazine. No. 1. Hersham: Ian Allan Publishing. p. 88–92. ISSN 1753-2469. OCLC 226087101.
- Grainger, Phil (January 2008). "DCC: The Way Ahead". Model Rail. No. 113. Peterborough: EMAP Active. pp. 40–41. ISSN 1369-5118. OCLC 173324502.
External links
[edit]