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Cannot read CV's (what does this mean?)

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  • Member since
    February 2002
  • From: Reading, PA
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Posted by rrinker on Tuesday, March 2, 2010 5:12 PM

 Zephyr seems to work fine - although the only decoder I haven't tried is a Tsunami. Everythign else has worked without a problem, QSI, Loksound, the old SOuntraxx LC series. Might be a difference between the at least 2 firmware versions there are for Zephyr, for those that have a Zephyr and can't program sound decoders. Both of mine have been the 'newer' version. And no I haven't enabled the "blast mode" either.

 I still rarely actually read anything. No need.

                                --Randy


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by scribbelt on Monday, March 1, 2010 10:37 PM

 Thank you for the additionnal infos, they are very useful and noted.

Serge

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Posted by maxman on Monday, March 1, 2010 10:46 AM

scribbelt

reading the cv will permit me to verify the "factory default" codes related to different effects (sound, speed etc.) on the loco.

But if I cannot read theses default codes, I can erase these codes by doing a reset and reprogram my own.

No, not exactly.  Being able to read the CV allows you to see what the current CV value is (assuming that the decoder supports CV feedback - some don't), regardless of whether the value in the CV is the default value or something you changed the value to.

You can change the default value to some other number, with the exception of a CV that identifies the manufacturer and maybe one or two more that they don't allow you to change.  However, you cannot change the default value itself since, by default, that would be the value that the CV would return to when you did a decoder reset.

For example, most decoders come with a short address default value of 3.  If you want the short address to be something else, you can change the short address CV to something else.  The decoder should remember this new number.  However if you reset the decoder, the short address will revert back to the default value of 3.  In other words, resetting the decoder will make all the CV revert back to what they were when they came out of the package, not what you changed them to. 

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  • From: Sierra Vista, Arizona
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Posted by cacole on Monday, March 1, 2010 9:53 AM

Practically every new decoder comes with an instruction sheet that explains which CVs are supported.  Most of those CVs were established by the National Model Railroad Association (NMRA) as standard, and are no different from one brand to another.  If you run across a decoder for which you don't have the documentation, you can nearly always find it on the manufacturer's web site.   As a general rule, CVs 1 through 95 will be the same for every brand.

As Randy suggested, it's always good practice to perform a factory reset before doing anything else to insure that the decoder hasn't been left in a scrambled form during factory testing.  I've ran into some that had extremely weird values in some of their CVs.  A factory default reset cures this problem.  The only time you may need to refer to the manufacturer's documentation to do this is to find out which CV is used for the factory reset and which value to program into that CV, because this was not part of the NMRA Standards.

Then you can begin changing things such as the address, start and stop momentum, start voltage, etc., which are always the same CV numbers because they are NMRA standard values.  The only exception you may encounter is a Marklin or some other European brand decoder that does not use NMRA Standards.

The main thing to consider at this time is to purchase the system which you like the most based on its features and user interface.  Don't worry about such technical things as whether or not you can read back CVs -- you can always find a way to do that later if you think it's really necessary.

  • Member since
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  • From: St-Lazare, QC.
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Posted by scribbelt on Sunday, February 28, 2010 10:22 PM

 Thank you all for the infos, they are greatly appreciated.

So please correct me if I'm wrong,

reading the cv will permit me to verify the "factory default" codes related to different effects (sound, speed etc.) on the loco.

But if I cannot read theses default codes, I can erase these codes by doing a reset and reprogram my own.

Did I miss something here or do I need more explanations?

Thank you.

Serge

  • Member since
    February 2002
  • From: Reading, PA
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Posted by rrinker on Sunday, February 28, 2010 8:01 PM

 I guess it depends on what you're doing. Once I program my decoders I rarely change them. I have a Zephyr so I can read back, but I rarely do so. First thing I do with a new decoder is reset it if it has that feature (all the ones I use have it). Then I know there are no wierd scrambled CV settings from factory testing or anything, and the address is 3. I don;t need to read the address, I know it's 3, so I just program in the address I want. My 50's era layotu does't have any fancy lights - no ditch lights, no rotary beacons, etc. so no need to read anything there. For speed matching, I do that in Ops Mode programming on the main, so there's no readback there anyway. If I have to adjust CV2,5 or 6 it's because whatever's currently in there is not right so I really don't care.

 And as much as I think DecoderPro is a great tool, I seldom use it. Again mainly because the programming my decoders need is very simple, no complex lighting setups, and also because I use, as much as possible, the same brand decoders for everything - so it's easy to remember the basic settings I do use.

                                               --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by jeffrey-wimberly on Sunday, February 28, 2010 5:59 PM

scribbelt
The Digitrax Super Empire Builder system is an interesting option, but I heard that it doesn't read CV's; the Zephir and the Super Chief do read them.

You heard right. The Super Empire Builder does not read CV's. The Zephyr, the Super Chief, etc do read CV's. Some will tell you there's no real benefit to being able to read CV's. Maybe they have systems that don't support it? With my Zephyr I can read a CV address and see just what function is mapped to that CV and decide whether or not I want to change it and it only takes a few seconds.

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Posted by cacole on Sunday, February 28, 2010 4:16 PM

Being unable to read CVs (Configuration Variables) makes programming of a decoder more difficult, but certainly not impossible.  Depending on the brand and type of decoder; i.e., sound or no sound, a decoder can have hundreds of CVs.  Normally, you need to program only three or four CVs on a non-sound decoder in order to get a locomotive to run like you want, and you don't need to be able to read CVs in order to do this.

If you have a system that cannot read CVs, you can use a free computer program called Decoder Pro and an interface device such as a Digitrax PR3 to read CVs and program the decoder.

As a general rule, you won't need to read CVs or use Decoder Pro until you become more proficient with DCC and want to set up a custom speed curve or adjust the CVs of a sound decoder.

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Posted by locoi1sa on Sunday, February 28, 2010 12:38 PM

 Reading CVs will give you a base line of what value is already in the CV. An example is CV2 start voltage. You want the loco to start moving at speed step 1 but you don't know what CV2 is already set to. Reading what the value is will give you an idea whether to increase or decrease the value to achieve the results you want. Not reading CVs is not a detriment. Sometimes I run across a decoder that fools the system and I get a Can Not Read CV on my program track. It does not mean you can't program it, it just means there is not a read back at that time. The decoder will take changes in programing.

    Pete

 I pray every day I break even, Cause I can really use the money!

 I started with nothing and still have most of it left!

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Cannot read CV's (what does this mean?)
Posted by scribbelt on Sunday, February 28, 2010 11:29 AM

Hello, I'm a newbie regarding DCC, I am looking to buy a walkaround system.

The Digitrax Super Empire Builder system is an interesting option, but I heard that it doesn't read CV's; the Zephir and the Super Chief do read them.

Can someone please explain me in plain words what this means, and is this a very important function.

Thank you. 

Serge

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