DCC Decoders and Indexed CVs

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 513-1024 (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 is 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 the convention is "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.

Question: when JMRI sends a command targeting CV2.257, does the packet structure sent reference a CV address of 257? or does it reference a CV address of 513? (ie 257+256)

In the case of SoundTraxx decoders, it sends a "write value of 2 to CV32", followed by the "read/write value of CV257".

CV32 is a special "secondary index CV" in the decoder.

Question: When JMRI sends a command targeting CV3.257, does the packet structure sent reference a CV address of 257? or does it reference a CV address of 769?  (ie 257+512)

In the case of SoundTraxx decoders, it sends a "write value of 3 to CV32", followed by the "read/write value of CV257".

QSI

QSI indexed CVs predate the S9.2.2 indexing specification and use CV49 alone or (CV49 & CV50) as subindexes to several other < 257 CVs.

ESU

ESU implemented indexed CVs as per NMRA S9.2.2, so you will see CVs like 16.2.384 in these decoder definitions.

ZIMO

ZIMO also followed the NMRA speciation.

SoundTraxx

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

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.

ISSUES
Several issues have arisen:

1. Some DCC systems have problems with CVs > 256. For example, an issue has been discovered 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 JMRI has been able to use the ESU algorithm successfully in DecoderPro. (But ZIMO provided different solutions with different firmware and as yet no JMRI volunteer has found time to resolve this). Unfortunately, SoundTraxx has not provided a similar workaround for its decoders.

Thanks to Dave Heap of Australia for a lot of this information.

 

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Walthers Bulkhead Flatcars 910-5800 Series Delayed

From Walthers:

We’ve been eagerly awaiting our first samples of the all-new HO Scale WalthersMainline 60' Pullman-Standard Bulkhead Flatcars (#910-5800 series) announced last year as part of the upcoming Steel Series. On every Walthers project, we inspect each step from the first set of CAD drawings to final delivery, to ensure you¹re getting the best possible models. Unfortunately, a problem encountered during the early stage of this project will require us to reschedule delivery to July 2021.

All other freight car models in the Steel Series are on time; additional updates on the Bulkhead Flatcars will be posted as information becomes available. While this is unwelcome news, we want to keep you informed, and rest assured we're committed to delivering high quality, satisfying model railroad equipment. We appreciate your support and patience as we resolve this issue.

Sincerely,

Your Friends at Walthers

 

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Custom Industrial Piping from Scratch

Ever have a need for industrial piping on your layout? There are many industries that use piping for one thing or another but the first one that usually comes to mind is the petrochemical industry. Ever take a close look at a refinery? There are pipes going everywhere. Take a look at Figure 1.

Figure 1 Refinery Piping

Piping is not limited to the petrochemical industry though, for example, what about a city waterworks, a paper mill, a power plant (be it Thermal, Nuclear or Hydro to transfer steam and water). Anywhere there is a need to transfer fluids/gases there is a need for some type of piping. Now, take a look at your model railroad layout and if you haven’t already thought about it where should there be some piping to make the scene more realistic?

What prompted this post was the author taking that look at his layout and noticing his heating oil distributor (which has a large oil storage tank on the other side of the tracks) having absolutely no piping in place. See Figure 2

Figure 2 Author's heating oil distributor

How exactly does that oil get from the storage tank to the distribution tanks, magic!?!? Having some piping in place not only would make the scene more realistic but also make it just plain look better!

The Problem

Now for the problem, there is a very limited number of kits out there that contain piping you could kitbash to fit into the scene I mentioned above let alone the right type of piping. Walthers does sell a couple of kits that contain piping and some pumps for it. Take a look at Figure 3 and Figure 4.

   Figure 3 Walthers part 272-130487

Figure 4 Walthers part 683-215

These are ok as long as what you need is contained in the kit. Hacking these up to fit your design is not easy and changing your design to fit these kits rarely, if ever, accomplishes what you wanted anyway and can be less than satisfying.

The Solution

So, is there a solution to this mess? Yes, there is! Plastruct has individual parts that allow you to build your piping solution exactly as you want it. An example is shown in Figure 5. This shows a distribution pipe flowing into a single feeder pipe complex. Think about it for a minute and you can see the possibilities. The additional bend in the lower right is just an elbow turned 90⁰ (to vertical). The wood blocks to merge the pumps can be bought at any local craft store and cut to size. They also serve as an interface between the different sized pipes. These styrene parts come in both white and black but obviously can be painted any color you wish including silver and even Testor’s chrome and then weathered a bit (piping doesn’t stay pristine for long).

       Figure 5 Plastruct Example Piping

You can download Plastruct’s Catalog and 2017 price list here.

The author hopes this will allow you to add a little more realism to your layout along with some additional fun time.

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