Issue
When setting up the TH90x series thermostats there are communication limitations.
Unable to pull multiple registers.
Some registers are only in Celsius, regardless of the display setting.
Product Line
EcoStruxure Building Operation, Field Devices
Environment
- SpaceLogic TH903 Series Thermostat
- SpaceLogic TH907 Series Thermostat
Cause
The TH903/TH907 does not support multiple/block register reads in Modbus.
The following parameters will show their value in Celsius only via Modbus communication regardless of whether the display is showing values in Celsius or Fahrenheit:
-
All SpaceLogic Series TH9xx thermostats
- Register 30 - Function Code 3/6 - Room Temperature (from the remote Modbus Controller)
- Register 1 - Function Code 4 - Actual Room Temperature
7 Day Programming Versions of TH900:
- Register 26 - Function Code 3/6 - 7 Day program schedule, heat set-point
- Register 27 - Function Code 3/6 - 7 Day program schedule, cool set-point
- Register 30 is used by the customer to override the current temperature. This register expects a value to be written to it every 15 seconds. If no values are written to it every 15 seconds, then it will populate with our internal temperature sensor value.
Resolution
Registers must be read one at a time rather than in groups.
When using Modbus write the set-point values in Celsius.
