Mars Modbus RTU serial communication (RS485) settings

Node Address, Baud Rate, and Data Format

Use the Mars web user interface, as outlined in the Mars User Guide, to change the Node Address (Unit ID or Slave ID), Baud Rate, and Data Format (e.g. number of data bits, stop bits, and parity bits) for serial communication  via Modbus RTU.

NOTE: Occasionally, after setting new Modbus RTU parameters such as baud rate and data format, the Mars unit will display the user's new selected parameters but will continue operating at previously set parameters. In this case, reboot the Mars unit to cause the new settings to take effect.

For a complete list of Mars Modbus registers and other Modbus information including supported baud rates and data formats, please see the Mars User Guide.

Scan Periods, Timeouts, and Delays

Please use the following settings on your Modbus client:

• Scan period  >= 1 second
• Timeout >= 500 ms
• Delay between polls >= 30 ms

Do not poll (scan) the unit more than once per second. Using shorter timeouts or higher polling rate may result in communication or timeout errors. 

NOTE: The parameters listed above are supported as of Mars firmware version  R5124 (May 2021). Older firmware versions required longer timeout settings of up to 3 seconds. For best performance, please update your Mars unit to the latest firmware. (See Mars Firmware Update.)