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Modbus communication with LC&D GR2400 lighting controller


Unable to get modbus to communicate with the automation server and LC&D GR2400 lighting controller.



Automation server



SmartStruxure Solution 1.5


The LC&D GR2400 lighting controller will ONLY allow 1 stop bit in it's modbus communication. Normally the stop bit setting in a modbus slave device is an "at least number", meaning the GR2400 should except 1 or more stop bits, but it does not.

The problem comes from the automation server by  default sends the 1 stop bit and addition "guard bits" for modbus communication. The guard bit setting was not available in versions prior to 1.5 and by default the automation server would send 3 stop bits causing the modbus communication to fail with the GR2400lighting controller.


  1. In SmartStruxure 1.5 right click on the Modbus Master Network and select properties.
  2. Click the advanced tab:


      3. Here you see the guard bit setting. This value should be a 0 if the automation server is to ONLY send 1 stop bit. If this number is left at default the automation server will add the number of guard bits to the user       setting of stop bits. By default that makes 3 stop bits from the Automation Server.

To properly communicate to the GR2400 the guard bit setting should be a 0 and the user selected stop bit should be a 1 in order to ONLY send 1 stop bit.

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