Guide to DCC Consisting
by Don Fiehmann
What is Consisting?
Operating and controlling several locomotives as if they were a single entity. For example, several diesels might be connected together to provide more power for a large train. Consisting is also called multiple unit lash-up, “MU-ing”, multiunit consist.
Many years ago, back in the DC days, at a model railroad club, I saw a long train going up a grade. In the middle of the train was a helper steam engine that stayed right in step with the train. I was impressed! With DC it was quite a task to get engines to run at the same speed when operating in a consist. I later found the secret ... the “helper” brass steam engine was a dummy with no motor or gear box! It was just another car in the train! DCC on the other hand has provided us many “tools” to make consisting work correctly. Speed matching allows engine speeds to be matched so they can run together as real helpers on a large train or grade. But there is even more to consisting in DCC.
DCC Consisting is implemented in three different ways: Basic, Universal, and Advance Consisting. Each type is different and each one has advantages and disadvantages.
It is using more than one decoder programmed with the same address. This is the simplest form of consisting. It could be like a pair of F7 units that are run together as a single unit, both with the same address. Another example is an engine with two decoders, one for sound and the other for motor and lights. This type of consisting is portable and can be moved to another DCC layout and operate correctly.
Uses the DCC command station to control the consist. Each engine in a consist is set up into the command station. The command station then signals all decoders in the Universal Consist to respond to one predetermined address. Most systems have a limited number of advanced consists (see your DCC system manual for details). This type of consisting works by sending out a command to each engine decoder in the consist. The command station needs to know the direction of each engine in the consist to be able to send the correct direction command. If you have three engines in a consist, three commands are sent by the command station each time. Since the information about this consist is entered into the command station and not the locomotive, it’s not portable and will not work on another layout without another set up.
A universal consist is deactivated up by using the command station. This should be done when not used to make room in the command station for other consists.
Advance consisting is the more modern way to use consisting. All mobile decoders today use CV19 as the Advance Consist address. This type of consist uses a two digit address of 01 to 127 (01 to 7F in Hex). Once a value other than 0 or greater than 128 is in CV19 the decoder will only respond to that consist address and commands. Speed commands to the normal engine address are ignored, but commands for lights and sound are accepted. Advance consisting is portable and should work on any DCC system layout.
One problem with advance consisting is that the two-digit range of addressing is the same as the standard two digit addresses. This could cause a conflict if you try to use a consist address that is the same as an engine using the same two digit address. If there is a value other than zero in CV19, the locomotive will not respond to its normal address, but the functions and lights will work. This is a simple check when a locomotive will not run that may have been consisted.
Checking Consisting Features
An easy way to check out consisting features is to setup the locomotive of interest as a one unit consist. Simply use program-on-the-main (PoM) to write an address into CV19. Then you can test the other CVs.
I have found that not all decoders respond correctly to the consist commands.