What is a Digital Command Control?
Command Control systems, both analog and digital, allow you to simulate prototypical train operation on your model railroad. With Digital Command Control you can operate multiple locomotives independently at the same time on the same section of track without a computer and without blocking or other complex wiring schemes. Digital Command Control systems use digital data packets to communicate commands to decoders that control locomotives and turnouts on the railroad.
What will it do for me and my railroad?
Simply put, DCC will let you "run your trains, not your track." DCC gives you the freedom to bring your railroad to life! With DCC you have truly prototypical operation at your fingertips.
Why use a digital system rather than an analog system?
Because digital technology gives extremely reliable operation and the technology is almost infinitely extendable without causing backward compatibility problems (analog systems are inherently more restrictive). Also, digital systems make wiring simple and easy to install. Because a digital system encodes information sent from the command station to the decoder as numbers grouped into packets, new types of packets can be added to a digital system to send more information thus extending the existing system without causing backward compatibility problems.
What is covered by the NMRA DCC Standard and RP's for DCC?
Only the basic communications protocols are covered in order to ensure interoperability and backward compatibility with existing systems. The Standard defines the signal sent over the rails, the tolerances allowed in its generation, the tolerances that must be accepted by the decoders and the basic communications protocol used to convey information to digital decoders. RP's cover things like the locomotive plug and "advanced" decoder features. Manufacturers are free to design and implement DCC hardware and interfaces that make sense for their customers. Manufacturers are also free to define how the DCC packets are handled by their system whether it be a simple command bus or a sophisticated network topology.
Was the NMRA DCC Standard based on the Lenz System? Isn't that a proprietary system?
After considering the various alternatives available at the time, the NMRA's DCC Working Group found that the signaling techniques used by the Lenz System had what they were looking for and used a communications protocol that offered the greatest future growth potential. While the signaling techniques were based on the Lenz design, numerous improvements were made and a packet format that is much richer in features was ultimately adopted. While the Standard has its roots in the Lenz system, it is not based on any proprietary equipment or information.
If you look at the early NMRA DCC working group FAQ's it was stated that the NMRA had a letter from Lenz confirming that there was nothing in the Standards that infringed upon any Lenz copyrighted, patented or proprietary information. In fact, as of June 24, 1996, this version of "the facts" is still on the DCC working group's web site. However, the latest word from the former head of the DCC working group is that the letter the NMRA has from Lenz talks about the market outside Europe. "For items sold within Europe Lenz GmbH does claim patents. It is the belief of the NMRA that you can develop a system that conforms to the NMRA standards that does not infringe on the Lenz patents in Europe but we have no letter from Lenz stating this nor do we have any legal opinion to back up that belief." Because of this conflict, analog mode conversion is NOT part of the NMRA Standards or RP's for digital command control.
What about other command control systems that have been around for a long time but are not DCC compatible? Why were these manufacturers left out of the process? What will happen to individuals who have invested heavily in these older systems?
According to the NMRA, all known command control manufacturers were contacted and invited to participate in the standards process. There is a general feeling among non-digital system manufacturers and users that they were left out of the process and were harmed financially by the adoption of the DCC standard. Indeed we have seen at least one previously successful command control manufacturer go out of business since the adoption of the Standard. Individuals who are running these non-DCC systems are really in the same position they always have been in that they have proprietary systems that are tied to a single manufacturer. These customers will continue with their existing equipment and will continue to be supported by the manufacturer of that equipment. New advances will continue to be made in these systems so it is not fair to call them "dead-end" systems. May avid proponents of DCC tend to look down their noses at non-DCC systems and feel that these systems are somehow inferior to DCC. Digitrax feels that this is absolutely NOT TRUE. NMRA DCC compatible systems are just one of many command control system choices available to modelers. Every command control system has good and bad points. The bottom line is that if you are satisfied with the system you have in place and your manufacturer is supporting you, there is probably no need for you to change systems. Digitrax Command Control encompasses NMRA DCC and other command control formats as well to give our customers the best of all worlds!
Won't the DCC Standard stifle creativity and technological advances?
It is important to realize that the standard only covers the communication protocol on the track. This protocol is very flexible and does not require any particular hardware. Just look at the innovations that have already occurred at Digitrax alone. We have developed and marketed automatic reversing boosters, decoders with 128 speed steps and user customizable speed tables, mobile decoders with onboard functions and lighting effects, stationary decoders with sophisticated routing and control logic and LocoNet, our communications network for model railroads. None of these things are included in the Standard but all are compatible with it. As long as the Standard is not extended further than the basic track level communications for train control, creativity will be encouraged rather than stifled.
Why not just standardize on an internal locomotive socket that allows any command control system to be installed?
The NMRA has already adopted an RP for standardized plugs in N, HO, and Large scales. Many new HO locomotives are now being made with this socket. Any command control manufacturer is free to make a decoder or receiver that will plug into this socket whether it is a DCC decoder or not; It looks like the HO socket will be successful in the long run. The N-scale socket that was adopted is based on a design from Germany and unfortunately only a few European manufacturers support this socket for their own decoders. In effect this RP for N scale means nothing to most of the European and the American N-scale market since the plug is not a practical solution for locomotives made by other manufacturers. The Large scale plug does not support all the functions usually present in these locos and even though LBG has begun using this plug, it may not ever by widely adopted in its present format.
Why are some things part of the Standard while other things are Recommended Practices?
First, let's look at the NMRA's definition of Standards, Recommended Practices and Data Sheets.
An NMRA Standard: "As charged by the NMRA CHARTER and CONSTITUTION, NMRA STANDARDS provide the primary basis upon which interchange between equipment and various North American Scale model railroads is founded. Under this requirement NMRA standards include only those factors that are considered vital to such interchange. For less critical matters see NMRA RECOMMENDED PRACTICES"
NMRA RECOMMENDED PRACTICES: "The RECOMMENDED PRACTICE category was established by the NMRA Board of Trustees in January 1957, to "a. Promote maximum interchange between and within units. b. Specify the details of major components to improve design and function. RECOMMENDED PRACTICES are only less mandatory then STANDARDS by virtue of their slightly less critical subject matter and or the fact that deviation for specific reasons is permissible."
DATA SHEETS: More specific information on such topics as Scenery, Trackwork, Operation, Electrical, Motive Poser, Rolling Stock, Structures, and other general items of interest.
In the case of DCC, the electrical information and the basic packet format are included in the standard as the primary basis for interchange between equipment. Other improvements to design and function that need to be considered if manufacturers choose to implement them are included in the RP's. These are things like the extended packet format and the locomotive socket.
Can I build a DCC system or any of its components myself?
Yes. There are commercial kits available and the DCC working group used to have plans available through the NMRA for building some DCC components yourself.
Where can I get a copy of the Standard and RP's? Can I participate in the DCC Working Group?
The standard and related Items are available on the NMRA Web Site. You can also find out how you can participate in these group discussions through the NMRA.
Page updated 6-21-00.