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CV 29 - bits and pieces - DCC - Tutorials - Getting You Started. - Your Model Railway Club
 Posted: Thu Apr 20th, 2017 11:26 am
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Location: Adelaide , Australia
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CV 29 – bits and pieces
For those of us “old school” DCC zealots (I never thought DCC and old school zealots would be together in a phrase), who remember life before the automated CV 29 converters; perhaps a word about the bits of CV 29.

There are still some decoders which resist the auto CV 29 converters, (Lenz decoders being one of them, as we will see shortly) and of course, there are still those of us who steadfastly stick to our Lenz systems. 

Lenz has appeal to me for their ability to supply a contiguous chain of hardware for use in computer control, where other brands need off grid bolt on stuff; but I digress.

CV 29 uses 8 subdivisions, or bits for control of some critical functions of motion decoders.

In most decoders the bits are numbered 0 to 7, while in Lenz they are numbered 1 to 8.

This numbering disparity doesn’t really affect the programming, as the bit value refers to the function you are trying to change, or vary – hence the thing we use to personalize our decoders (vary the configuration of), is called a Configuration Variable or CV.

In daily use, there are 6 bits of CV 29 which we use for basic control, viz:-

·        Motor direction; forward or reverse.

·        14 or 28/128 speed steps.

·        DCC or DCC/DC

·        Railcom on or off

·        Use of speed tables (CV 67 to 94) or three step settings (CV 2 6 and 5).

·        2 digit addresses 1 to 127 (CV 1); or 4 + digit address 128 > (CV 17 and 18). 

It’s NOT possible to change one bit by itself.  Each time we want to change a bit, the total values of all of the bit integers must be re-entered.

Here’s a table which shows us what we need . . .

So, if a decoder has a value of zero for CV 29, then the motor will go forward, the throttle will be 14 steps, DC will be off, Railcom will be off, the three step control will be on and the loco will only be able to have a two digit address.  Perversely 2 digit addresses go up to 127.

Now, if we want the motor to go forward when we select forward on the throttle (0), we want to use 128 speed steps (2), DCC only (0), Railcom to be off (0), a speed table (16) and a 4 digit address (32); if we add 2 + 16 + 32 = 50 – that’s the number to enter into CV 29 to make those three changes happen.

If we decide later to only use CV’s 2 6 and 5 for speed control, then the value for the speed table (16), is subtracted from the 50, becoming 34 which is the integer entered into CV 29.

Simple, yes?

For those who have got this far and now have a migraine, I’ve attached a chart which will solve every problem.

Just set CV 29 to 0.  Add up the integer values for the combination of facilities you desire and enter them into CV 29.

Happy Throttling.

Attachment: CV 29.xlsx (Downloaded 5 times)

Port Elderley
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 Posted: Thu Apr 20th, 2017 11:22 pm
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Joined: Sat Oct 19th, 2013
Location: Reston, Virginia USA
Posts: 3555

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Hi All,

CV29 is a real rag-bag of bits (should that be bytes?). There is a handy calculator at that allows you to determine what the value of CV29 should be. many of the changes are made automatically from the Powercab handset (128/28 steps, short or long address). 128/28 steps and DC mode are different, either or both can be selected.


©Nigel C. Phillips
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