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4-6 COMMUNICATION PROTOCOLS CHAPTER 4
DC-24 and DC-25 operation manual
4.3. PROTOCOL MODBUS RTU - Word for RS-485
This protocol allows the user to communicate with devices using the protocol Modbus RTU
This protocol uses the function 06h to write and the function 03h to read data from the
display. The data block is a Word. The user can write or read data. If the data must be sent,
the sensor mist be disabled modifying the parameter 3. See paragraph 3.3.3
“Parameter 3
for RS-485: Sensor control and communication protocol
”
The temperature is sent multiplied per 10 when writing or reading. As an example
21,6 ºC will be sent as 216 (00D8h)
To write the temperature value, the data must be sent to register 0000h (40001). The data
format must be 16-bit word format. In the following example, the data block structure is detailed
for a 19,7ºC (00C5h) temperature writing.
Func. Reg. H Reg. L Data Low CRC High CRC
06h 00h 00h 00h C5h 48h 7Bh
To write the humidity value, the data must be sent to register 0001h (40002). The data
format must be 16-bit word format. In the following example, the data block structure is detailed
for 57% (0039h) humidity writing.
Func. Reg. H Reg. L Data Low CRC High CRC
06h 00h 01h 00h 39h 19h FAh
If the data block is correctly received, the display responds with the same data block it
has received
If there is an error in the reception, the display responds with an error detection block with the
following data.
Addr. Error Error code CRC low CRC high
86h
The possible errors are:
02 = CRC error.
To read the temperature value, the data request must be sent to register 0002h
(40003). In the following example, the data block structure is detailed for a temperature request.
Addr. Func.
Start
Addr. H
Start
Addr. L
Num.
Reg. H.
Num.
Reg. L.
Low CRC High CRC
03h 03h 00h 02h 00h 01h 24h 28h
If the block is correctly received, the display responds with the temperature value in 16-
bit Word format. Remember that the temperature is multiplied per 10.