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XW-110™ WiFi Temperature Sensor Users Manual Modbus/TCP (XW-110-Plus only)
5.4 Read Sensors – Modbus Function Code 03 (0x03)
The Read Holding Registers function is used for the temperature sensors.
Request
32-bit sensor values are read from 16-bit register pairs. Consequently, senors addresses and registers
must be even numbers.
Vin Start Addresses
Start Address: 0x0010 (Vin)
Input Quantity: 0x0002
Temperature Sensor Start Addresses
Start Address: 0x0110 (Sensor Input 1) to 0x0114 (Sensor Input 3)
Input Quantity: 0x0002 to 0x0006
Response
32-bit floating-point values are returned, either as little-endian or big-endian numbers, depending on the
configuration in the
WiFi Networks tab.
With little-endian ordering, a temperature reading of sensor 1 (0x0110) would return 0x800042A2. The
least significant word would be 8000 hex and the most significant word would be 42A2. This
hexadecimal value converts to a temperature reading of 81.25 degrees.
If a temperature or humidity sensor is not installed, a value of 0xFFFFFFFF (NaN) is returned. Other
inputs will show measured values of the open circuits.
Errors
Sensor Read Error Function Code (1 byte): 0x83
Exception Codes (1 byte):
0x01 – Function not supported.
0x02 – Incorrect combination of start address and input quantity
Xytronix Research & Design, Inc. Page 41