Can One Change CV29 Value Using a Function - LokSound?

[SRman]

I have an ESU LokSound v3.5 that developed a fault. It works perfectly going forwards, but there is no drive in reverse and the sounds run away (no load). It currently has sounds for a T9 4-4-0 and is fitted into  Hornby model, on which I have not fitted a front coupling, so the need to reverse it is not great but it would be useful on occasions (my layout has continuous runs).

 

I had an idea last night that if I could swap the power feed to the brushes using a switch, I could run in reverse. Then I thought that a physical switch is a bit inconvenient, and would require lifting the model simply to get it to go backwards, so I progressed to thinking about an electrical/electronic switch that could be operated by a function output from the decoder. Then the idea hit that even this is getting over-complicated, and all I need to do is reverse the feed through CV29, by adding or subtracting 1 to or from its value. So. the question is, is this possible to do by assigning a function in the decoder?

 

If I could do this, I could simply drive the loco forwards to where it has to pick up a train, then hit a function (let's say, function 4), and it will instantly add 1 to whatever is in CV29. The loco would then move backwards even though the controller still says forwards (I have NCE Power Cabs and Pro Cabs).

 

Any takers?

 

Please note, I am posting this exact text on multiple forums. If you have a solution, it is entirely up to you whether you post answers in all forums you are a member of (to reach slightly different audiences with some overlap of their citizens), or choose to answer on just one. In that sense, apologies if members of the multiple forums keep seeing the same question.

[SRman]

I wouldn't be surprised if you are correct regarding CV29, but it's not quite true that CVs can't be reprogrammed by using functions. How else can volume be changed on the fly using function buttons, as some sound projects do? Even so, the ability to reprogram may only apply to certain CVs, which may not include CV29.

I can easily do POM but even that is probably a bit long-winded when simply trying to change direction for a short burst, but that may well be my only option.

I have used POM on the fly to change sound volumes while a train is actually running.

Thanks for your answer, though. Much appreciated.

[Removed a/c]

Maybe I am not grasping your request but what would the difference be in changing CV29 so it works correctly and having a function button set?  

[RAF96]

As stated certain CVs can be reprogrammed on the fly on the main, such as acell/decell, Hornby Sapphire coal/water 'refuel' and as above volume settings.

 

Please consider this -as some people have installed a relay to allow a function to switch smoke units on the move, why can you not use a latching relay under control of a function to 'reroute' your motor wiring twixt decoder and motor, rather than attempting to fiddle with CV29.

 

Edit: A thought - do you have 128 speed steps set both at the decoder and the controller as some sound decoders will not work correctly without.