Modbus communication examples - DMP5 - DMP6 - DMP7 - DMP8 - DMPX

DMP Series User Guide

Document code
M212357EN
Revision
D
Language
English
Product
DMP5
DMP6
DMP7
DMP8
DMPX
Document type
User guide

Reading dew point temperature value

Device address used in the following examples is 240 (F0hex).

Measurement values returned by the device change depending on ambient conditions and/or device settings.

Request Response
Bytes on the line (hexadecimal) Description Bytes on the line (hexadecimal) Description
(silence for 3.5 bytes) Start of Modbus RTU frame (silence for 3.5 bytes) Start of Modbus RTU frame
F0hex Probe address F0hex Probe address
03hex Function (Read Holding Registers) 03hex Function (Read Holding Registers)
00hex Register address 04hex Number of data bytes
06hex FDhex Value of first register (least significant word)
00hex Number of 16-bit registers to read (2) F9hex
02hex 41hex Value of second register (most significant word)
31hex Modbus RTU checksum 72hex
2Bhex 4Bhex Modbus RTU checksum
(silence for 3.5 bytes) End of Modbus RTU frame 14hex
(silence for 3.5 bytes) End of Modbus RTU frame
Communication description
Register address 7 (1-based Modbus documentation format) = 0006hex (0-based format used in actual communication).
Data format Two 16-bit Modbus registers interpreted as IEEE 754 binary32 floating point value, least significant word first.
Returned value 4172FDF9hex, which is binary32 representation of 15.187 (°C Td).

Writing pressure compensation value

Request Response
Bytes on the line (hexadecimal) Description Bytes on the line (hexadecimal) Description
(silence for 3.5 bytes) Start of Modbus RTU frame (silence for 3.5 bytes) Start of Modbus RTU frame
F0hex Probe address F0hex Probe address
10hex Function (Write Multiple Registers) 10hex Function (Write Multiple Registers)
03hex Register address 03hex Register address
00hex 00hex
00hex Number of registers to write (2) 00hex Number of 16-bit registers written (2)
02hex 02hex
04hex Number of data bytes 54hex Modbus RTU checksum
6Ehex Value for first register (least significant word) ADhex
14hex
44hex Value for second register (least significant word) (silence for 3.5 bytes) End of Modbus RTU frame
75hex
4Ehex Modbus RTU checksum

The response to a write function informs that the function was correctly received by the device. It does not guarantee that the written value was accepted by the device (for example, in case out-of-range values).

To verify that the value was really accepted by the device, read the register value after writing.

ABhex
(silence for 3.5 bytes) End of Modbus RTU frame
Communication description
Register address 769 (1-based Modbus documentation format) = 0300hex (0-based format used in actual communication).
Data format Two 16-bit Modbus registers interpreted as IEEE 754 binary32 floating point value, least significant word first.
Value to write 44756E14hex = 981.72 (hPa)