KB943: Functions on Mobile Decoders

This article was last updated on Oct. 18, 2010, 6:10 p.m. | Print Article | Leave Feedback

Digitrax decoders have outputs that can control lamps and other on/off devices installed in your locomotive.  These are called functions.  Functions are things like: lamps, sound units, smoke units, etc. All Digitrax decoders are equipped with two or more function outputs that are used to turn functions on and off.

Decoder function outputs can be:

1.   Leads (wires) attached to the decoder that are used to hook up external functions.  See Table I below for wire color codes used on Digitrax decoders.


2.   Pre-wired function outputs that hook up by just plugging in the decoder. This is the case for decoders that come with lights attached to the decoder.


3.    Solder pads on the decoder that allow you to solder wires to hook up functions to the decoder.

Some decoders have more than one form of function output. For example, the DN163K0a has two function outputs pre-wired to the white LEDs on the decoder and 4 additional solder pads available for adding wires to hook up more functions.

Additional Functions

If you are planning to operate more functions in addition to headlight control you will need to use a decoder with more function outputs. For applications where you are using a sound module, you will want a decoder with at least 4 or 5 functions. Function only decoders, like the TL1, TF2 & TF4, are also available if you wish to add even more functions.

Function Types

There are five types of functions available on Digitrax decoders:

1. Standard functions turn functions on and off. Many Digitrax decoders with standard functions offer head lights that can be set up to be either automatically reversing or individually controllable.  Digitrax decoders are shipped with automatic reversing head lights enabled.  Click here if you want to disable this feature.  When you are using a standard function output, simply hook up the function output to the function device and you will be able to turn it on and off from your throttle.

2.   Standard* functions turn functions on and off. These decoders offer automatically reversing head lights only.  With this type of function output, no additional function configuration is possible.  When you are using a standard* function output, simply hook up the function output to the function device and you will be able to turn it on and off from your throttle.

3. Configurable strobe (CS) functions can be set up to run as simple on/off or as single or double pulse strobes.  This option is available only on a few Digitrax decoders where limited code space would not allow FX or FX3 functions to be added.

4.  FX functions incorporate generators for prototypical lighting effects, like Mars lights, ditch lights, Gyralites, random flicker, single & double pulse strobes, etc.

5. FX3 functions incorporate FX generators with additional dynamic and static qualifiers.  FX3 functions are fully remappable so they can be controlled by any function key on your system.  A master light switch can be set up to turn off all lights on a locomotive. Functions associated with advanced consists can be controlled, too.

Function outputs on Digitrax decoders are available in several current ratings depending on the decoder.  See the decoder specifications for your specific decoder to determine the current rating of the function outputs.

What the wires are for

Wire Color

Power Pick-up Right(Engineer's Side)


Power Pick-up Left(Fireman's Side)


Motor + Right Brush


Motor Left Brush


F0(Fwd)-Forward Light


F0(Rev)-Reverse Light


Lamp Common


F1-Function 1


F2-Function 2


F3-Function 3


F4-Function 4

White w/ YellowStripe

F5-Function 5

White w/ Green Stripe

F6-Function 6

White w/ Blue Stripe

Note: DH82 & DN92 decoders used a different wiring color code.  Please check decoder spec sheets for the wire colors used with these decoders.

How many functions does your decoder support?

F0 (FWD), F0 (REV), F1, F2, F3, F4, F5, F6, F7, F8, F9 and so one are each counted as one function.  This is an industry wide convention.  Check the decoder index for your decoder to determine how many functions it supports.

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