Modbus communication examples - OPT100

OPT100 User Guide
Document code
M211858EN
Revision
V
Language
English
Product
OPT100
Document type
User guide

Reading acetylene value

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

The values returned by the device differ depending on the measurement conditions. Your device may not return the same values.
Request
Bytes on the line (hexadecimal) Description
(silence for > 3.5 bytes) Start of Modbus RTU frame
F0hex OPT100 address
03hex Function (Read Holding Registers)
00hex Register address (Acetylene)
16hex
00hex Number of 16-bit registers to read (2)
02hex
30hex Modbus RTU checksum
EEhex
(silence for > 3.5 bytes) End of Modbus RTU frame
Response
Bytes on the line (hexadecimal) Description
(silence for > 3.5 bytes) Start of Modbus RTU frame
F0hex OPT100 address
03hex Function (Read Holding Registers)
04hex Number of data bytes
40hex Value of first register (least significant word)
40hex
00hex Value of second register (most significant word)
00hex
0Ehex Modbus RTU checksum
E8hex
(silence for > 3.5 bytes) End of Modbus RTU frame
Communication description
Register number 23 (1-based Modbus register number) = address 0016hex (0-based address 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 40400000hex, which is binary32 representation of 3 (ppm).