Indexed CVs - Soundtraxx

A big thanks to NCE Super User - Dave Heap for help on this topic.

***Important Note** for the Powerhouse, Power Pro, PH-Pro and CS02 you must use OPS mode programming / (POM) Programming On the Main for making indexed CV changes.  If you have a Power Cab system there's no problem. It doesn't have the firmware problem.

Soundtraxx video on YouTube -


CVs with dot in the number (1.300) are “Indexed CVs” Which is a fancy way of saying it is really a group of three CVs that need to be changed like a combination lock.

The first two numbers “unlock” the CV you need to program. The third number is what you are really changing.

  1. Ensure CV 31 is set to a value of 16.
  2. Enter a value of 1 into CV 32 to select Indexed CV Page 1.
  3. Select CVs 257-512 from your command station.

From page 13 of the attached Soundtraxx manual:

Indexed CVs The term “indexed CVs” tends to cause confusion and consternation. Simply put, indexed CVs are located on ‘pages’ to help manage the total number of CVs. This is required by the NMRA DCC Standard and works like this: Indexed CVs are accessed with the use of two CVs: CV 31 enables indexing when set to a value of 16 (the default value) and CV 32 selects the desired indexed page. You do not need to type “1.” Into the command station when programming indexed CVs. Because of the number of features and options contained within Econami decoders, three pages of indexed CVs are provided: To access CVs 1.257-1.512: 1. Ensure CV 31 is set to a value of 16. 2. Enter a value of 1 into CV 32 to select Indexed CV Page 1. 3. Select CVs 257-512 from your command station. To make things easier, Econami CVs are grouped by like function as follows: CVs 1.257-1.512 are used for configuring Flex-Map function mapping CVs. CVs 1.257-1.384 are used for function mapping CVs and CVs 1.385-1.512 are used for automatic effect configuration. Refer to “Configuring Function Mapping” for more information.


Indexed CVs (and Power Pro)
Indexed CVs are a way to have more CVs than just those available in the range 1-1024 inclusive (a limit set by the DCC packet standards in S9.2.1). Many of these are already reserved for particular purposes.
However the NMRA standards covered that need and provided for a way to allow for many more CVs. This is intended to be done by a page indexing system for CVs in the range 257-512 inclusive, allowing for in excess of 16 million CVs.
The NMRA standard S9.2.2 covering Configuration Variables defines the following:
- CVs 1-256 (inclusive) and 512-1024 (inclusive) are to be treated as normal CVs.
- CVs 257-512 (inclusive) are to be treated as paged index CVs, with the page number being stored in CVs 31 and 32 (the index registers).
What this means is that there are a total of 65,536 possible pages of CVs 257-512, so you need to set the correct values in the index registers before accessing any CV in this range.
In JMRI we chose the convention "CV a.b.ccc" for these NMRA-compliant indexed CVs, where "a" is the value to load in CV31, "b" is the value to load in CV32 and "ccc" is the desired CV number (in the range 257-512) on the page specified by "a" and "b" combined.
QSI indexed CVs predate the S9.2.2 indexing specification and use CV49 alone or (CV49 & CV50) as sub indexes to several other <257 CVs.
ESU implemented indexed CVs as per NMRA S9.2.2, so you will see CVs like 16.2.384 in these decoder definitions.
ZIMO also followed the NMRA speciation.
SoundTraxx has now implemented S9.2.2 style indexed CVs in its Econami and Tsunami 2 ranges. But they use a fixed value of 16 in CV31 so only quote the value in CV32. So you will see CVs like 1.257 in these decoder definitions.
TCS adopted an even more complex system using CVs 201, 202, 203 & 204.
It is important to realize that indexed CVs are still just CVs as far as your DCC system is concerned. It knows nothing about indexed CVs.
But several issues have arisen:
1) Some DCC systems have problems with CVs>256. For example, I discovered an issue in the NCE Power Pro firmware that causes the wrong CV to be written in Program Track mode for any CV>256.
2) It appears that some decoder brands may have problems processing indexed CV calculations inside the decoder within the timing specifications of the NMRA standards. This can potentially cause issues with some brands/models of DCC system.
3) ESU and ZIMO both provide in-decoder workaround solutions for problem (1) and we have been able use the ESU algorithm successfully in Decoder Pro. (But ZIMO provided different solutions with different firmware and as yet no volunteer has found time to resolve this). Unfortunately SoundTraxx has not provided a similar workaround for its decoders.
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