KB878: 14, 28 or 128 Speed Steps-Why?

This article was last updated on May 8, 2012, 2:16 p.m. | Print Article | Leave Feedback


This article was originally posted on this site in 2006, but the source material dates back much further than that, probably back to the early 1990's, when DCC was an emerging control system. The article discusses non-sound mobile decoder programming operations. Many of the issues discussed in this article are less relevant when using recently produced decoders, but this text still does cover some questions which may be raised when you are using mobile decoders which were manufactured by other companies. These decoders will operate in the Digitrax environment, but you may need to make some adjustments.

The earliest Digitrax mobile decoders, the DN82 and the DH82 were designed to operate in 14, 28 or 128 speed step modes. The first Digitrax Starter Set, Challenger, operated in either 14 or 28-speed step modes.The Big Boy Set, which superseded the Challenger in 1998, was able to operate in 14, 28 or 128-speed step modes. This continued with subsequent Digitrax command control sets until the first Chief Set, which defaulted to 128 speed step operation.


Since all Digitrax command systems now operate in the 128-speed step mode by default, if you have a locomotive fitted with an earlier decoder, you can "Status Edit" that locomotive's address to operate in 14 or 28 speed step mode. Status editing gives you the possibility of operating a variety of locomotives that are fitted with different decoders.

Status editing is a command station operation, that lets you tell the command station to send 14 or 28 speed step commands to a specific decoder address.
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DCC-Sometimes it seems like we are separated by a common standard

Digitrax Command Control systems use the default-mode of 128-speed step operation and use the Paged programming method. These defaults were chosen so that customers who use Digitrax decoders with Digitrax systems will have the best performance out of the box without having to change anything but the decoder address.

Not all DCC decoders are created equal! The DCC Standard & Recommended Practices (RP's) specify 14, 28 & 128 as options for the number of speed steps that decoders and systems may support. For this reason there are a variety of decoders on the market that support 14, 28 and/or 128-speed steps. Digitrax decoders support all speed step options; the factory default is 128 speed step operation.

Not all DCC decoders support the same programming options specified by the DCC Standard & RPs. The specified methods are:

  • Paged programming

 

  • Direct programming

 

  • Physical register programming

 

  • Operations mode programming


All Digitrax decoders support paged programming and physical register programming. Some Digitrax decoders support direct mode programming as well. The Digitrax default method of programming is Paged mode.

Because these differences are allowed by the Standard and RP's, you may find that a decoder made by manufacturer X, when used with a command control system made by manufacturer Y may need to be reprogrammed to work with that particular system. This may seem to be an "incompatibility" but it really isn't, you just need to know the options and how to configure them to work with your particular combination of components. This application note will explain how to handle decoders made by other DCC manufacturers with your Digitrax system.

Programming DCC Decoders

Be sure that the command station you are using is sending programming information in the right mode for the decoder you are using

Many non-Digitrax decoders use only Physical Register programming mode i.e., Registers r1, r2, r3 up to r8. [Note: this is not common with today's decoders, Ed.] If you are programming a non-Digitrax decoder with your Digitrax system, be certain that you have selected the programming mode that the decoder will understand. You won't be able to program a decoder that uses only physical register mode with paged mode and vice-versa. When you enter programming mode with your Digitrax system, you will see PAGE in your LCD as the default programming mode. If the decoder you are programming requires physical or direct programming, you will need to follow the instructions in your system manual to change to the mode required before you proceed with programming.

Status Editing

Status editing matches the number of speed steps which your decoder can understand with the number of speed steps the command station is sending to it. On some occasions, you have programmed the decoder address and you are ready to run your loco on your Digitrax system but "OH NO, it won't GO!" You might still have to tell the command station that the decoder at the set address does not understand the 128 speed step step language that is the Digitrax default.

First, always try to run your decoder in 128 speed step before you status edit. Many non-Digitrax decoders will understand 128 speed step mode. If the decoder won't run with 128 speed steps you will need to do what we call a Status Edit. This means that you will tell the command station to send 14 or 28 speed step commands to the decoder. If you know how many speed steps the decoder is set up for just perform the steps detailed in the Related Articles (below). If you do not know, then begin with 14 speed steps and if that turns out to be incorrect, you will notice that the headlights will blink each time you advance the throttle. If you notice a blinking headlight then status edit again for 28 speed steps and the problem should be solved.

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