Vaisala HPP272 User Manual

A.5 Modbus Communication Examples
Reading H
2
O
2
Concentration Value
Device address used in the following examples is 240 (F0
hex
).
The values returned by the device dier depending on the ambient conditions
and/or device settings. Your device might not return exactly same values.
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
F0
hex
HPP272 address F0
hex
HPP272 address
03
hex
Function (Read
Holding Registers)
03
hex
Function (Read
Holding Registers)
00
hex
Register address 04
hex
Number of data bytes
00
hex
D4
hex
Value of first register
(least significant
word)
00
hex
Number of 16-bit
registers to read (2)
7A
hex
02
hex
43
hex
Value of second
register (most
significant word)
D1
hex
Modbus RTU
checksum
E8
hex
2A
hex
33
hex
Modbus RTU
checksum
(silence for 3.5 bytes) End of Modbus RTU
frame
AB
hex
(silence for 3.5 bytes) End of Modbus RTU
frame
Communication Description
Register address 1 (1-based Modbus documentation format) =
0000
hex
(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 43E8D47A
hex
, which is binary32 representation
of 465.65997 (ppm).
HPP272 User Guide M211972EN-B
58

Vaisala HPP272 Specifications

General

Brand	Vaisala
Model	HPP272
Category	Measuring Instruments
Language	English