Function Mapping

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Summary: Function Mapping determines which keys on the throttle control a function. The functions can be remapped if needed, in some cases multiple functions can be assigned to a single key. See your decoder manual for which Configuration Variables are used for the function map, and how to alter them. The CVs which are used for function mapping a limited to 8 bits, therefore only 8 functions can be mapped to a key.

Why Remap Functions?

There are several reasons for remapping a function.

  1. Standardize functions among different brands of multifunction decoders:
    • As OEM will change supplies of multifunction decoders over time, and may offer different decoders in different locomotive, function remapping gives you the ability to have a consistent function key usage over a number of different decoders in your motive power fleet.
  2. Simplifiy Button Presses
    • With the advent of decoders supporting more than 10 or twelve functions, the number of keys on the throttle to control them was exceeded. To solve this many DCC manufacturers began adding a shift key functionality to their throttles. Much like a computer keyboard where pressing Control or Control-Shift gives access to alternate characters.
    • Unfortunately, that usually means having to press multiple buttons to access F11 or F28. Which can be confusing. In some cases, a key or key combination is needed to access the function. The result is that the full complement of functions is ignored in favour of the bell and whistle

Function Remapping

Remapping the functions gets around the issue of multiple key presses or key combinations to achieve a result. Fortunately more manufacturers support remapping in their decoder software. Others have included automation, where activating one function key triggers several functions.

Some functions may offer limited options for remapping, such as F0, F1 and F2 (lights, bell and whistle).

Planning Your Function Map

The easiest way to accomplish function remapping is to plan which functions will be assigned to each key in advance. Do that using a spreadsheet. Refer to the manufacturer's instructions to determine what is possible and how the default function map is laid out.

Begin by selecting the functions desired, and the key which they will be mapped to.

The Function Matrix

CV # Function Description 14 13 12 11 10 9 8 7 6 5 4 3 2 1
33 FL(f) Forward Headlight X
34 FL(r) Reverse Headlight X
35 Function 1 X
36 Function 2 X
37 Function 3 X
38 Function 4 X
38 Function 5 X
40 Function 6 X
41 Function 7 X
41 Function 8 X
42 Function 9 X
43 Function 10 X
44 Function 11 X
45 Function 12 X


CVs 33 through 37 control outputs 1 through 8, and cannot be remapped outside of that range (indicated by the grey sections.
CVs 38 – 41 map to outputs 4 – 11
CVs 42 – 45 map to outputs 7 – 14


To remap the function the process is simple. To remap function 4 to function 6 do the following:

Referring to the matrix above (or the one supplied with the decoder)

  1. Determine the value of CV 38 (Function 4)
  2. Write this value into CV 40
    1. Write a value of 6 into CV 40

To map multiple outputs to a single function key:

  1. Map Functions 9 and 12 to Function 9
    1. Determine the values for F9 and F12
    2. F9 = 11 and F12 = 14
    3. The sum of those values is 25
  2. Change the value of F9 (CV 42) to 25


With the level of sophistication in multifunction decoders increasing every year, software tools such as DecoderPro make the remapping much easier. For ESU multifunction decoders, consider the LokProgrammer as well.

Further Reading