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Modbus Map

We distribute a constants file called "ljm_constants.json" that defines all information about the Modbus register map.  The dynamic filter & search tool below pulls data from that JSON file.

  • Name:  A string name that can be used with the LJM library to access each register.
  • Address:  The starting address of each register.  Valid through LJM or with direct Modbus.
  • Details:  Click to get text pulled from the description field in the JSON.
  • Type:  Specifies the datatype, which also tells you how many registers each value uses.
  • Access:  Read-only, write-only, or read & write.
  • Tags:  Used to associate registers with particular functionality.  Useful for filtering.

For a U3/U6 with firmware less than 2.0, or for the UE9, see the deprecated Modbus system called UD Modbus.



Could somebody please make this list available as Excel sheet of PDF.


If you want something you can browse, search, or even print, I suggest you use "ljm_constants.json" which is on your computer if you have run our installer.  This is a text file so you can open it in about anything.

The other thing we can do is use our internal autoscribe software to generate a printable modbus map.  See if the new Printable Modbus Page is useful, and if so we can fill in the rest of it.