Are your JMRI decoder files up to date

With all the new decoders out there have you been keeping your decoder definition files up to date? The volunteers at JMRI regularly add new and update old decoder definition files. These files contain all the various CVs and settings for each decoder. This is a big job since there is a file for just about every decoder ever manufactured. When you initially install JMRI on your computer it should also include the decoder definition files for all decoders up to that time. However as manufacturers add new decoders, new decoder definition files have to be created, so you will occasionally want to add new decoder definition files.

Fortunately you don’t have to download and reinstall the entire JMRI package every time you buy a new decoder, you can just import the new file–here’s how. First go to the JMRI website to get the new file. Unfortunately they don’t make it easy to find them. They are stashed at . While you can import the file directly from this directory I find it easier to download the decoder definition file to my computer first. This is especially true if you are using an older computer not connected to the internet. To download the file just right click on it using your mouse and select “Save as” or “Save target as” and then indicate the directory where you want it. With newer versions of DecoderPro you can read it from anywhere on your computer but on older versions (2.3.5 and earlier) it needs to be in the “program files/JMRI/XML/Decoders” directory. Also, if you double click on the file name it will open it and what you save will not be a valid xml file. If you get a message that the file is not a valid xml file when you try to install it, this is why.

Once you have the file downloaded open DecoderPro and click on the files menu option. Then click on the import decoders file option. A window should open allowing you to select the directory where the file is located–select it and begin the import. This can take a little while so be patient–a popup message will let you know when it is complete. For older versions of DecoderPro the import option can be found under the debug menu option.

One other tip I want to pass on is that when you download and install an updated version of JMRI it will also install all the new decoder definition files for you. However, if there is an older version of a file already in the decoder database the program will not overwrite it. You have to go into the preferences, delete the file, then run the “Rebuild decoder index”. There is a popup that tells you that a different version of the decoder file already exists in the database so you can go back and make the deletion.


  • Larry, When JMRI indicates an old decoder file was not written over, what is the benefit of having the newest file for
    an old decoder? Second, if the newest file is downloaded, does this mean re-programing the old decoder once again and
    creating a new locomotive decoder file?

    • Joel—the main reason I can see is if they fix an issue. Also some manufacturers might have one decoder definition file for all their locos whereas another one might release a new file for each decoder version or locomotive. I cannot imagine these not being backwardly compatible though.

      As for needing ti reprogram the loco that may depend on the eason for the new version, but in most cases I would think not. The only time I have had o reprogram a decoder was when I had some WOWSound decoders upgrade to a new version.

  • Great info of something that is not obvious.