This week’s post is a ‘how-to’ about DCC decoders and identifying which ones you have.

As DCC (Digital Command Control) is becoming evermore popular, second-hand locomotives already fitted with DCC decoders are becoming more frequent on websites such as eBay.  It’s easy to grab a bargain but what have you actually bought?  Normally they are just listed as DCC-fitted, leaving it fairly ambiguous as to what’s inside.  Sometimes you can remove your locomotive shell and then see the make and model on the decoder.  But if it was a tricky or custom install it may not be that simple to see.

So why does it matter what the decoder is?  Just about all DCC decoders have the same basic functions, such as motor control and lights, but some are far more advanced than others and have hidden talents.  That being said the one primary thing people change is the address of the decoder, normally to match the number on the locomotive: most DCC systems have that ability no matter what the make or model of the decoder. But if you want to alter any other functions or features which the decoder may have, you will need to know what decoder you’ve got.

This can be done fairly simply by reading the value of CV8 from your decoder.  Now that isn’t as daunting as it sounds and I’ll explain how to read your decoder in a moment.  CV stands for Configuration Variable and it’s these which allow decoders to be set up how you want them.  Different CVs are allocated for different things, for example, CV3 is for Acceleration Rate or Acceleration Momentum.  The higher the value stored in this CV the slower the locomotive will accelerate.  But how do you know which CV is for what?  Well the NMRA (National Model Railroad Association) foresaw this could be a problem and have developed a set of standards for manufactures to follow.  You will notice on all reparable DCC products it will say ‘NMRA compatible’.  This means that all the systems will work with each other so you can use different make decoders and locomotives all on the same layout.

All these CVs can be read using most DCC command stations. This normally involves placing your locomotive on your programming track and selecting the CV Read function.  Depending on which DCC command system you have will depend on how this is done so you will need to look at your instruction manual.  It will ask you which CV you want to read and by selecting 8 it will return a three digit number.  This number will be the unique manufacturer number of your chip.

Again the NMRA control this. They have a list, which can be found here, which has all the manufactures of NMRA complaint DCC products listed by name and by identification number.

So for example if the number was 101 then you have a Bachmann Trains decoder.

Manufactures tend to keep the features and functions the same across their product ranges, so downloading a manual from the manufacture’s website should give you the information you need to set up your decoder.

But what if the decoder in your locomotive is an older model? And companies usually make more than one type of decoder.  To help with this the NMRA have allowed CV7 to be used as a version number by the manufacturers.

So, for example, if your decoder has a CV8 = 129 and CV7 = 49 then you have a Digitrax decoder from the ‘Series 3 with FX3’ family.  There are lots of different decoders in this family but the controls are the same so any instruction manual for a ‘Series 3 with FX3’ will give you what you need.

The NMRA do not list the contents of CV7, as this is down to the manufactures, which can make it a bit tricky to find the information.  But once you know the manufacturer, from CV8, you could email their help desk with the CV7 number and they will be able to help.

Checking the decoder type in your second-hand locos is a good idea because you may be missing out on some great features you never knew you had.