What are the Modbus communication specifications for the communicating thermostat models?
The communicating WME423 models (with 'm' in the part number) use Modbus RTU protocol with a baud rate of 9600, no parity, and CRC error checking. The Modbus address range is 01~31 (default 1), configurable in Installer Setup Item 1. The thermostat supports multiple read/write parameters including temperature, fan status, system mode, and valve outputs through defined Modbus address table registers. (Page 6-7)
From the official Honeywell Thermostat Set Temp manual, page 6
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