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Extended Function Mapping

YouChoos Resouces

The Purpose of Function Mapping

There is an NMRA standard for mapping decoder functions to buttons in DCC, and these are supported by all CT Revision 4 decoders too. However, the NMRA standard only defines how the first few functions can be mapped, as it was developed before any decoders appeared on the market with many more functions. The SL51-4, for example, provides 8 physical function outputs which can be used for things like lighting, smoke units, couplers/decouplers and just about any other electrical device you can dream up which could fit in the train.

On top of those physical function outputs, you also have the callable sound effects which you may want to control with the press of a button. There are up to 16 such sound effects available for this purpose, plus you need a button to switch the main running sounds on and off.

Just to top it off, Function Keys can also be assigned for other specialist purposes, such as the hidden Low-Beam feature, which causes temporary dimming of lighting outputs for a timed period when an FKey is pressed! There are one of two other hidden features akin to this too, but we won't go into detail here!

So, in total if you need a lot of function keys! This means CT have had to provide some non-standard CVs to allow for a wider mapping range.

CV(s) Purpose Comments
33-46 NMRA standard function mapping These CVs follow the standard NMRA guideless for how CVs should be mapped.
163-176 CT extended function mapping

A combination of CVs from 33-46 and 163-176 provides full mapping of up to 8 function outputs and sound effects, as well as shunting mode and main running sounds. You really need to calculate the values for both ranges of CVs at the same time to map the functions properly.

To help you calculate the correct values for the desired function mapping, you can use the table below. Each Function Key has 2 CVs associated to it, and by setting the corresponding bits in each of those 2 CVs you can define which functions/sounds that key controls. A single function key could control multiple actions if you wanted it too, such as synchronising a firebox light with the sound of coal shovelling.

For decoders that have less function outputs (SL76 has 4 for example), thesecan be mapped in exactly the same way, although obviously there is no point in setting any functions to activate the non-existent outputs!

16 Effects, or 8 Effects?

CT have implemented the 16 sound effects in a rather interesting manner, which is good for controllers that only have 12 function buttons. Basically there is no way to use anything beyond F12 with the CT decoders which seems rather limiting until you discover the 'ALT' function. ALT is a special function that can be assigned to the function key of your choice, and allows you to switch between 2 banks of 8 sounds.

So, as an example let's say you assign ALT to the F4 key... you could then map sounds 1-8 to keys F5-F12, giving access to the first 8 sound effects, but with F4 switched on, means that F5-F12 access sounds 9-16 instead! Brilliant!

Downloadable PDF and Word DOC formats of this table, with an example mapping can be obtained at the bottom of this page.

Sound 8/16 Sound 7/15 Sound 6/14 Sound 5/13 Sound 4/12 Sound 3/11 Sound 2/10 Sound 1/9 ALT Engine on/off Shunt AUX7 AUX6 AUX5 AUX4 AUX3 (purple) AUX2 (green) AUX1 (yellow) AUX0 (white) FKey CV
128 64 32 16 8 4 2 1 F0 fwd 33
128 64 32 16 8 4 2 1 F0 fwd 163
128 64 32 16 8 4 2 1 F0 rev 34
128 64 32 16 8 4 2 1 F0 rev 164
128 64 32 16 8 4 2 1 F1 35
128 64 32 16 8 4 2 1 F1 165
128 64 32 16 8 4 2 1 F2 36
128 64 32 16 8 4 2 1 F2 166
128 64 32 16 8 4 2 1 F3 37
128 64 32 16 8 4 2 1 F3 167
128 64 32 16 8 4 2 1 F4 38
128 64 32 16 8 4 2 1 F4 168
128 64 32 16 8 4 2 1 F5 39
128 64 32 16 8 4 2 1 F5 169
128 64 32 16 8 4 2 1 F6 40
128 64 32 16 8 4 2 1 F6 170
128 64 32 16 8 4 2 1 F7 41
128 64 32 16 8 4 2 1 F7 171
128 64 32 16 8 4 2 1 F8 42
128 64 32 16 8 4 2 1 F8 172
128 64 32 16 8 4 2 1 F9 43
16 8 4 2 1 F9 173
128 64 32 16 8 4 2 1 F10 44
16 8 4 2 1 F10 174
128 64 32 16 8 4 2 1 F11 45
16 8 4 2 1 F11 175
128 64 32 16 8 4 2 1 F12 46
16 8 4 2 1 F12 176

HINT: For document links below, either open them directly in your web browser by clicking the links, or right-click and save target instead...

Download PDF of SL51-4 Extended Function Mapping


Experiences & Commentaries

YouChoos Resouces

HINT: For document links below, either open them directly in your web browser by clicking the links, or right-click and save target instead...

YouChoos commentary on various decoders    
YouChoos Products

Build your own sounds for CT decoders

YouChoos no longer supplies CT products, but if you are interested in obtaining a license for the YouChoos/CT SoundProg software, this is still available, costing £25 for a single PC license. Note that no further maintenance is planned.

The software was developed by YouChoos and runs on a PC enabling you to build, manage and load your own sound projects into CT sound decoders!

Build your own sounds for CT decoders Costs only £125

Required parts:

  • CT SoundProg device (not supplied)
  • UK power supply (not supplied)
  • Serial-to-USB cable (can be supplied by YouChoos on request)
  • YouChoos' own software for creating, managing and loading sound projects to CT decoders (included in &25 license)
  • Full documentation (supplied digitally)

Download Software

Download Software

Anyone can try out this software for free by downloading the latest version from here. A license key is required to save projects, or to load them into a decoder.

User Guide

Download User Guide (PDF)

Download the User Guide for the YouChoos CT SoundProg application here.

Version History

Enhancements and Fixes

View Version History here, for a list of enhancements and bug fixes.

The YouChoos CT SoundProg application provides an easy-to-understand interface for configuration of CT Elektronik sound decoders, including an intuitive design for almost all aspects of the decoder's features - not just sound. Take a look at the screen shots below to get an idea of how powerful and simple this is...

Project details Edit individual CVs DCC loco address
Motor tuning and speed settings Function Outputs Steam sound schedule
Diesel/Electric sound schedule Callable sound effects Sound configuration
Function Key mapping Update decoder Firmware or load sound project