Speed steps in a decoder

[model-trains]

Is there a quick and easy way to know how many speed steps a loco decoder has?

 

Is it possible to find out from the CV tables?

 

Can it be assumed that DCC Locos with sounds have 128 steps?

 

Is it possible by checking the decoder inside the loco, I have never opened a loco and would prefer not to.

 

I look forward to your replies guys, thanks in advance.

 

Paul

[RFS]

The default setting for most decoders is 28/128 speed steps. Which of these it's using is set in the command station and not in the decoder.

 

Decoders can also have 14/27 speed steps, but this is set in the decoder in CV 29. 

[tarifa]

CV's are not related to speed steps, RFS  explains the situation.  I don't agree the setting of speed steps is achieved through CV29, this CV controls the motor functions i.e. forward or reverse, operation on DC systems etc.  Decoder manuals explain the utilization of CV29.

 

Some time ago I compiled a chart of speed steps for both ESU and Zimo sound files.  You may find it useful.  Feel free to amend it as required, it is not perfect and you will need Excel to read it.

 

Speeds-Threshold Settings.xlsx

 

Mike

[WIMorrison]

CV29 is very relevant to speed steps as you use this to make the decode use 14 steps and also set a complex speed curve. The best way to understand CV29 is to use this calculator 

 

http://www.2mm.org.uk/articles/cv29 calculator.htm

 

 

[cravensdmufan]

1 hour ago, tarifa said:

CV's are not related to speed steps, RFS  explains the situation.  I don't agree the setting of speed steps is achieved through CV29, this CV controls the motor functions i.e. forward or reverse, operation on DC systems etc.  Decoder manuals explain the utilization of CV29.

 

Some time ago I compiled a chart of speed steps for both ESU and Zimo sound files.  You may find it useful.  Feel free to amend it as required, it is not perfect and you will need Excel to read it *.

 

Speeds-Threshold Settings.xlsx 34.48 kB · 5 downloads

 

Mike

Thanks for sharing your file with us.

 

(* My OpenOffice 4.1.3. opened it perfectly). 

 

Now all I have to do is get my head round it!  I have an Loksound v5 which behaves strangely at certain speed steps so I must check it out.  Yet another job on the ever increasing "to do" list.

[WIMorrison]

Unfortunately it uses 128 speed steps and there are actually only 126 speed steps available to increase rot decrease the speed of a loco ;)

[Crosland]

1 hour ago, tarifa said:

 I don't agree the setting of speed steps is achieved through CV29,

 

It is, but only in an arcane way.

 

In the beginning speeds were sent using 4 bits, giving 16 values for emergency stop, stop and 14 speeds.

 

By moving the bit that controls the directional lights a new scheme using 5 bits (32 values) for the speed was created, Stop and emergency stop are duplicated leaving 28 speed steps. How the decoder interprets the speed command is set by bit 1 of CV29. To be pedantic, this bit is not 14 v 28/128 steps. It actually tells the decoder where to look in the command for the bit controlling the directional lights. The assumption is that a decoder using the alternate light control will also implement 28 speed steps.

 

If the command station is sending 28 speed steps and the decoder is set for 14 speed steps then the directional lights will go on and off with changing speed as the decoder will interpret the extra speed bit as the light control.

 

Then a whole new set of commands were added that allow for 128 speeds. This requires the command station to be able to send the new commands and the decoder to interpret them. To be pedantic, and consistent with the original nomenclature, this is actually 126 speed steps plus stop and emergency stop. A decoder that supports 128 steps will respond to 128 step commands sent from the command station regardless of CV29 bit 1.

 

Any recent decoder (sound or not) will (should!!!) support 128 speed steps.

 

 

[model-trains]

Thanks guys, this forum is brilliant.

 

Let me put my question another way if I may.

 

Would it be reasonable to assume, in most cases, unless tinkered with, a loco will be set for a 126/128 step decoder and if it has a smaller step decoder then CV29 will have already been adjusted?

 

But when I use iTrain it requests I add the decoder type, 14, 28, 128 

How do I know what step type decoder is installed in each loco?

 

Paul

Edited September 26, 2020 by model-trains

[Kaput]

You read CV29 and the result into the backcalc box in the above CV29 calculator.

 

That tells you whether the decoder is set to 14 or 28/128. Thats all you can do without identifying the specific decoder. Generally speaking ESU decoders default to 14 out of the factory (most sound project makers alter the default to 28/128) and everything else I've ever used defaults to 28/128.

 

Choosing between 28 and 128 on a decoder with CV29 set for such is done on the controller and is usually down to personal preference.

Edited September 26, 2020 by Kaput

[WIMorrison]

1 hour ago, model-trains said:

...

 

But when I use iTrain it requests I add the decoder type, 14, 28, 128 

...

 

Paul

 

iTrain offers you the choice of 14, 28 or 126. You decoder will either be set to 14 speed steps or 28/128 as defined in CV29. 

 

if the decoder is 28/128 then you can choose either 28 or 126 in iTrain, the difference is immaterial as if you choose 28 speed steps you set the step size to 1, if you choose 126 then you set the step size to 4 - therefore the result is effectively identical.

[Nigelcliffe]

3 hours ago, Kaput said:

You read CV29 and the result into the backcalc box in the above CV29 calculator.

 

That tells you whether the decoder is set to 14 or 28/128. Thats all you can do without identifying the specific decoder. Generally speaking ESU decoders default to 14 out of the factory (most sound project makers alter the default to 28/128) and everything else I've ever used defaults to 28/128.

 

Err,  not quite.   The CV29 setting in an modern ESU "out of the factory" implies 14 step.  But the ESU decoder is meant to interpret what it sees on the track, and automatically decide what to use (described in the ESU manuals).    But, ESU do several things a bit differently to everyone else.

 

 

- Nigel

[Suzie]

In i-train it is reasonable to assume that all locos are 126 speed steps, since this is most likely the case. If you have a decoder so old that it does not support 126 speed steps you will most likely know about it - there are not many of them around and you would not use one unless you really, really had to.

 

You will need to ensure that CV29 is set correctly in all locos to make sure that the directional lighting works correctly too.

 

In the unlikely event you find a loco not responding to i-train then you will need to investigate whether it supports 28-steps instead, or maybe 14/27-steps (most 14-step modes are actually 27-steps in practice - they are fully compatible with one another and generally you will find performance very similar to 28-step).

 

All sound decoders are 126-steps. This mode was around long before sound decoders appeared.

 

 

Edited September 27, 2020 by Suzie

[model-trains]

I was expecting most of my locos to be 126 (128) step decoders, the ones that I considered could be either the 126 or a lesser step decoder are

- Hornby Digital Loco Class 08 0-6-0 R1236-Shunter-

- Hornby Northern Rail twin cab DMU Class 142

- A Sprinter DMU Class 150

 

I had no concerns for the larger, newer, loco's, with or without sound.

 

I guess the mind says 08 shunter, no sound, small loco, maybe doesn't need 126 step decoder but being digital I guess equally it could be.

 

The main area here, for me, was I was looking for an easy way to check and know what decoder was in each loco and expected to find that in the Cv's. 

 

Thanks everyone for your help.

 

Paul

[Suzie]

I don't think any UK loco manufacturer has released a decoder without 126 speed steps, even though some have had pretty rotten decoders.

 

The Roco crane is I think the only RTR decoder fitted item that came with a 14-step decoder, and that was decades ago. The 28-step spec and 126-step spec came at about the same time, so there are very few, if any 28-step decoders that don't also support 126-steps.

[tarifa]

17 hours ago, Crosland said:

 

By moving the bit that controls the directional lights a new scheme using 5 bits (32 values) for the speed was created, Stop and emergency stop are duplicated leaving 28 speed steps. How the decoder interprets the speed command is set by bit 1 of CV29. To be pedantic, this bit is not 14 v 28/128 steps. It actually tells the decoder where to look in the command for the bit controlling the directional lights. The assumption is that a decoder using the alternate light control will also implement 28 speed steps.

 

 

Thanks Andrew, I learn something every day.  But I should have read the book.

Mike

[pauliebanger]

4 hours ago, model-trains said:

 

The main area here, for me, was I was looking for an easy way to check and know what decoder was in each loco and expected to find that in the Cv's. 

 

 

 

You can read the value in CV8. This is a unique manufacturer's code which you can then look up in this list here:

 

https://www.nmra.org/sites/default/files/standards/sandrp/pdf/appendix_a_s-9_2_2.pdf

 

It will not tell you what speed steps are set, but the respective manufacturers' manuals will have details about what is possible. (and may show the default setting.

 

Best regards,

 

Paul

[model-trains]

7 minutes ago, pauliebanger said:

You can read the value in CV8. This is a unique manufacturer's code which you can then look up in this list here:

 

https://www.nmra.org/sites/default/files/standards/sandrp/pdf/appendix_a_s-9_2_2.pdf

 

It will not tell you what speed steps are set, but the respective manufacturers' manuals will have details about what is possible. (and may show the default setting.

 

Best regards,

 

Paul

 

 

Thanks Paul

 

I am aware that the manufacturers details and decoder type are in CV 8 and 7

 

I have picked up so far CV8 

Hornby Hobbies 48

Electronic Solutions 151

 

But I also have a n Evening Star where the manufacturer is 193 which I don't see in the PDF?

 

A very handy sheet you have shared though Paul, thank you.

 

Paul

[jpendle]

21 minutes ago, model-trains said:

I am aware that the manufacturers details and decoder type are in CV 8 and 7

CV 7 is firmware revision, not decoder type, some manufacturers do have a CV set which tells you the decoder type. For example Zimo use CV250 to tell you the precise decoder, MX617, MX600, etc.

 

Regards,

 

John P