NMRA DCC Consisting

The following section describe the NMRA DCC terminology and methods for all of the various forms of Decoder Consisting and discusses the advantage and disadvantages of each type.

Depending on the DCC system you use, these NMRA terms may not all make any sense.  The DCC system may have ALTERNATE NAMES for the same exact form of consisting clearly leading to potential confusion.  It you want to know more about what DCC system uses what terms for consisting, go here: Consisting Term Confusion
This link also includes my reference information or basis for the NMRA consisting terminology at the bottom.

It should be noted that the ACTUAL usable address ranges offered by a given DCC system manufacture is sometimes artificially limited and can vary from system to system. Check with the system manual for the supported range.


CV DEFINITIONS AND NOTES:

1) CV1 = Short Address (2 Digit Address)  1-127 is the actual NMRA range. Short Address "0" is not allowed to control a individual DCC decoder.

2) CV17/18 = Long Address (4 Digit Address or Extended Address) 0 to 16,383 is the actual NMRA range. 

3) CV19= Advance Consist Address which uses a Short Address with all its limits. The maximum number of consist possible is 127 but the system may limit the number. NOTE: The use of a Short Addresses means Advanced Consisting takes AWAY an available Short Address for use by a non consisted single locomotive. If a single engine has a short address that is the same as an active advance consist address, it will become part of the consist automatically no matter what.


NMRA CONSISTING DEFINITIONS

Address Consisting (Using CV1 or CV17/18)   Decoder Based


1) Decoder Based.  All the locomotives in the consist have their normal Short or Long address set to be the EXACT same number on the Programming track.  
2) Only one DCC speed command from the Command Station is required to control entire speed of all the engines in the consist.  This keeps trains response to throttle commands high with no erratic starts.
3) Locomotive orientation will require using CV29 Direction bit to control locomotive running backwards in a consist going forward. 
4) Some do not consider this consisting simply because nothing special is involved per say. But is perfectly valid none the less.
5) This form of consisting IS portable as in it can be moved to any layout with no preprogramming or reprogramming.

Advantages: Does not require any special consisting capability from the DCC system.  This form of consisting IS portable for it can be moved to any layout with no preprogramming or reprogramming.

Disadvantages:  A) Creation, deletion, or changes to any given consist must be done through preprograming or reprogramming.  B) Each locomotive that becomes part of the consist loses its ability to operate as a independent engine including its functions.  Everything you do is global to all the engines within the consist.  Example: Turn on the headlight, every headlight in the consist turns on.  Not prototypical.  C) All the engines must be facing the same direction when becoming part of the consist or you must preprogram or reprogram CV29 to customize any engine facing backwards.  If you do that and you move the consist to another layout, you must remember the engine orientation when you put it back together.


Basic Consisting  
(Using CV1 or CV17/18)     Command Station Based
 
1) Command Station builds a list in its memory of all the locomotive addresses that are part of the Consist. 
2) Command Station must sends a unique DCC command to each and every locomotive in the consist to control the entire consist.  It has the same command load effect as if one was running the same number of locomotives independently. 
3) Command Station must keep track of each locomotive's orientation in the consist and adjust each DCC command accordingly.

Advantages:  A) Each Engine retains it's individuality at all times.  You can take any engine from one layout to another and it will respond correctly on that specific layout with regards to being in a consist or not.  B) You can select any locomotive and control its functions independently of the consist.

Disadvantages: A) This form of consisting IS NOT portable and will not automatically transfer to any layout.  The new layout will have to rebuild the consist from scratch.   B) On a large layout with lots of running trains, response to throttle commands can suffer.  As more engines are running, the DCC system naturally gets slower and slower in responding to throttle speed changes since it has to send so many unique DCC speed commands.  When the DCC system gets overloaded, speed changes can result in erratic jerking between engines in the consist as they accelerate or decelerate.


Advance Consisting 
 (Using CV19)   Decoder Based
 
1) Command station programs decoder's CV 19 with a short address called the "Consist Address" using OpsMode (Programming on the main). 
2) Only one DCC speed command from the Command Station is required to control the entire speed of all the engines within the consist.  Train response to throttle commands is the same as a single engine and does not suffer from erratic operation during speed changes.  Performance will always be better than Basic Consisting on large layouts.
3) Locomotive's direction is under CV19 control to allow each locomotive in the consist to run backwards or forwards as needed to work together in the consist.

Advantages: A) This form of consisting IS portable for it can be moved to any layout with no preprogramming or reprogramming.  B) On a large layout, train response performance does not suffer.  C) You can select any locomotive in the consist using it primary address and activate any functions.  D) You can optionally customize what happens to F0 to F8 functions using CV21 and CV22 when function commands are sent to the consist address.  

Disadvantages: Uses up one short address for each Advanced Consist you create.  This is not a problem if your DCC system allows you to use long address below address 128.

NOTE for people who use or wish to use a computer to setup Advanced Consisting::  CV19 is meant to be controlled by the DCC command station and configured dynamically during operations of trains.  Advanced Consisting should not be done on the programming track because there are special DCC commands for "on the fly" Programming of CV19 on the main line.  These special DCC commands allow the decoder to properly process the CV19 information without requiring any formal programming and can resolve any other internal issues as required to make everything transparent.  Do not use a PC program to setup CV19 because such action bypasses the command station.  Why?  Some DCC systems will activate additional feature and functions that ONLY work when you setup the consist with the command station.  Otherwise the consist will not operate as expected like all the other consist that have been setup by the command station.
   

Unified Consisting (Using all CV's)   Combination of above

1) Both Basic and Advance consisting are used at the same time to manage a single larger consist made up of other smaller consist.
2) Each individual Advance consist remains intact at all times
3) This form of consisting has all the advantages and limitations of Basic and Advanced consisting combined.

Advantages:  Example:  A train, with multiple engines in an Advanced Consist on the point, needs to have a "Helper Consist" added to it to go up a grade.  The Helper Consist, itself is an Advanced Consist, is coupled to the train.  Using Basic consisting, a new consist is created that temporarily combines both Advanced Consist (main and helper) into a new single consist.  The engineer then uses the new basic consist to bring the entire train, with helpers, up the grade.  At the top, the Basic consist is deleted.  The helpers, now independent again, are free to run back down the hill.  The train itself, also independent again, resumes its trip using the original consist address it had when it arrived at the bottom of the grade.