# Making a DCC engine change directions



## Mister Bill (Jan 30, 2014)

I need your help.

I have a Digitraxx DCS51 and I can do most anything I need to do.

At a train show, I purchased a matched set of MRC DCC F’7 A’s. Both units run under the road number 101. The lead unit is lighted with sound, and the second unit has DCC only and no lights or sound. When coupled, the units run back to back and the noses are pointed in opposite directions. Both run forward and backward properly in prototypical form.

I want to unlash these two and run each as unrelated and separate A units and add lights and sound to the unit that is presently without.

How can I get the unlighted soundless F7 A to run forward when it is programmed to run backwards in the consist with the other F7 unit? It will be re-numbered 282 when re-done.

Is it a programming option, or can I just reverse motor wires?

Bill


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## fcwilt (Sep 27, 2013)

You need to change the value of the configuration register CV29.

If it is an ODD number you need to SUBTRACT 1 and make it an EVEN number.

If it is an EVEN number you need to ADD 1 and make it an ODD number.

The reason is the the first bit of CV29, which can have a value of 0 or 1, determines the direction a loco moves in response to a throttle command.

The value 1 is normally used to indicate the loco should respond to forward by going backwards and reverse by going forwards.

This allows having two A units running back to back and yet both move in the same direction.

Since your trailing A unit is already working that way this bit is likely set to 1 BUT if someone simply wired the motor in reverse the bit may still be 0.

In any case changing the current state of the bit to the opposite state will take care of running the trailing A unit by itself.

You may find this of interest as it allows you to determine the value of CV29 for various settings:

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

Frederick


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## Brakeman Jake (Mar 8, 2009)

They may have the same value in CV 29 and still run in opposite directions if previous owner has tuned them using "advanced consisting" if these decoders have this option,obviously.That would explain why the lights are off on the trailing loco.

For most decoders,CV 19=0 should break the consist then the locos will need individual addresses to run solo.


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## Magic (Jan 28, 2014)

Probable the easiest way to do this would be a factory reset. CV8 to 8 
in most cases but newer MRC decoders uses CV125 to 1 check CV8 for manufacturer ID for 143 (MRC)
This will set the loco right and the address to 3, readdress to 282

Doing this will remove all speed matching settings but if you're not going to run an AA set no big deal.

If both locos are address to 101 I don't think you can advanced consist them.

Magic


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## Mister Bill (Jan 30, 2014)

Thanks. I am working on it.

As a side note, the reason I cannot lash these two together is that they run at different speeds and one slows down the other to a halt.

I am not trying to solve that problem.

It just added to my frustration.

I hope a reset will cure everything.

I worked on it for a while and was getting nowhere. I tried re-setting 29 and then a factory reset. Nothing. Then I noticed one of the programming track wires had become unsoldered.

I have to take a break. 

Too much information.

Thanks again, 

Bill


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