# Digitrax Decoder Help



## DavefromMD (Jul 25, 2013)

I just installed a Digitrax DH126D decoder in a Walthers Trainline F40PH locomotive.
It supports 28/128 step speed tables.

Programmed it to take the defaults in start, mid, and max voltage and 28 step speed.

When I run it, it maxes out at step 14. No increase in speed after that.

So I went back to set startup at 25, mid at 128, and max at 255.

Same result - maxes out speedwise at step 14.

Step 14 seems to be about half the speed of its max when it was just DC.

Other locomotives doing fine.

I have an NCE Power Cab system. 

Any ideas?


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## D&J Railroad (Oct 4, 2013)

DavefromMD said:


> I just installed a Digitrax DH126D decoder in a Walthers Trainline F40PH locomotive.
> It supports 28/128 step speed tables.
> 
> Programmed it to take the defaults in start, mid, and max voltage and 28 step speed.
> ...


CV5 if the max speed. CV6 is the mid point speed. Yeah, its reversed from what it seems it should be, but hey, we're just the users tryin to figure this stuff out.
Set your CV5 to 255 and CV6 to the lower setting of half throttle. CV2 is your starting voltage (range 0-255) and ya only use that for motors that need a bit of throttle to get started. CV65 (range 0-9) is the kickstart for step one on throttle dial to get motors turning over.


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## DavefromMD (Jul 25, 2013)

That's what I have set up - CV5 is set to 255, CV6 to 128.

I get the same response speedwise whether I change it back to the defaults or use these settings. I get no increase in speed after step 14 and step 14 is about half of what its DC full speed was.


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## fcwilt (Sep 27, 2013)

Double check that you have 28 speed steps enabled in the decoder.

Do you have to set this Power Cab system to use 28 steps?

Are you wanting to use the speed tables?


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## DavefromMD (Jul 25, 2013)

It set up for 28/128 speed steps.

The Power Cab controller is also set for 28. My other locos respond fine.

I don't want to use custom speed tables and have that option turned off in the CV.


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## fcwilt (Sep 27, 2013)

This decoder has a "switching" mode which reduces that max speed - sounds like that mode may have been activated.


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## rzw0wr (Aug 28, 2013)

If I remember correctly.
The CVs for Start, Mid and Top speed are a ratio.
128 is 100% of the voltage.
example; 13/128 = 10%
64/128 - 50%

you have your mid (CV6) set at 100%.
CV5 set at 200%.

I can't explain the lower speed from DC to DCC.


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## DavefromMD (Jul 25, 2013)

Yes it is a ratio and the top is 255 according to the Digitrax decoder manual. 

It has to do with binary numbers and bits. There are 2 bytes allocated to CV 5. Two bytes is 8 bits. In binary the number can be only 1 or 0. So 11111111 (8 ones) = 255.

If you remember working with different base numbers in math, you'll grasp what I'm talking about.
Yeah, I'm a computer geek, so I understand this.


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## rzw0wr (Aug 28, 2013)

Just repeating what I read.
I understand binary, hexadecimal and octal.


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## fcwilt (Sep 27, 2013)

DavefromMD said:


> ...There are 2 bytes allocated to CV 5. Two bytes is 8 bits....


Two bytes = 8 bits????


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## DavefromMD (Jul 25, 2013)

"Two bytes = 8 bits????"

Oh, oh. Brain lock. You got me. Ahem, of course there are 8 bits in a byte!

"Just repeating what I read."

Out of curisoity, where did you read that the top value is 128. That sounds like it might be from 14 step speed.


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## rzw0wr (Aug 28, 2013)

Dave, I don't remember.
I was read up on DCC CV programming earlier this year and I remember reading it.
It may have been the stepping tables, I can't really remember.
I thought it said all speed CVs.
I looked on the internet and can't find it.

I do remember it was from an individual and not from a company. 

I could be way off.
I guess I need to start checking my information sources before commenting.


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## fcwilt (Sep 27, 2013)

Did you check to see if the decoder was running in "switcher" mode? 

According to the documents this reduces all speeds by (appx) 50%.


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## fcwilt (Sep 27, 2013)

There are a couple of CVs that often default to 128 - these are the Forward Trim and Reverse Trim. 

Perhaps this is the source of the 128 value that poster was thinking of.

The CV2, CV5 and CV6 settings, of course, range from 0 to 255.


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## rzw0wr (Aug 28, 2013)

I think I got something mixed up somewhere.
I can't find it now.
All I remember is that the article said that 128 was 100% of the voltage and setting this CV above that did nothing.

Maybe a senior moment.


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## Magic (Jan 28, 2014)

128 speed steps is not the same thing as CV values. 
255 is max (100%) setting for that CV. 1 is the lowest.
If I remember right 0 is also 100%?????

The computer will go through 28/128 steps to get to max speed. 
CV 02 is start current. CV 6 is max speed and CV 5 is mid range. 

fcwilt may have it with the switching mode. 

Magic


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## DavefromMD (Jul 25, 2013)

Another strange symptom is that whe I set a start up voltage to 12 (5% power), it starts quickly but when it gets to 3 it slows back down to almost a stop then accerates up from there again. This is with mid set at 150 and max at 255. 

Where is the setting for switcher mode? Someone else mentioned that but I can't seem to find where that is set. It cetainly sounds logical. It would be odd for that to be the default, but I could have accidently set that without knowing it.


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## DavefromMD (Jul 25, 2013)

I found where the switching speed setting is - CV54. I also found in the manual for the decoder the various values that are used and what they do in CV54. It does not come up in the standard setup using NCE Power Cab. I assume then I have to go directly into CV programming to see what this is set at. I know I didn't go in and change this, so it will be interesting to see what the default is or at least what it is set at now. It would seem odd if this got reset in the standard programming setup, but you never know.

While I'm at it, CV54 also controls torque compensation. Can anyone give me a good simple explanation what this does? The explanation in the manual isn't clear to me.

Torque Compensation (according to the manual) has a relationship with PWM. I have seen that setting and if I understand correctly relates to how silent the operation of the decoder and motor is? So for more silent operation, do you set that value low or high? (0 - 255, actually 1 - 255 as it appears 0 is the default and 0 = 255).


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## fcwilt (Sep 27, 2013)

By default (if memory serves me) the switching mode is toggled with F6.

But it should be in the documentation.


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## DavefromMD (Jul 25, 2013)

OK, F6 is off. When I toggle it on a 6 shows up on my LED display.
I checked the value in CV54. It is 64 which has switch speed off, Torque Compensation on, decoder lock disabled.

Any other ideas?


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## fcwilt (Sep 27, 2013)

At this point I would try a decoder reset and see if the problem still exists.


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