Vaisala DRYCAP DMT143 - Modbus Communication Examples

A.5 Modbus Communication Examples
Reading Dew Point/Frost Point Temperature 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 the 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
Transmitter address F0
hex
Transmitter address
03
hex
Function (Read
Holding Registers)
03
hex
Function (Read
Holding Registers)
00
hex
Register address 04
hex
Number of data bytes
06
hex
F5
hex
Value of first register
(least significant
word)
00
hex
Number of 16-bit
registers to read (2)
96
hex
02
hex
C0
hex
Value of second
register (most
significant word)
31
hex
Modbus RTU
checksum
E7
hex
2B
hex
D9
hex
Modbus RTU
checksum
(silence for 3.5 bytes) End of Modbus RTU
frame
56
hex
(silence for 3.5 bytes) End of Modbus RTU
frame
Communication Description
Register number 7 (1-based Modbus register number) = address 0006
hex
(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 C0E7F596
hex
, which is binary32 representation of -7.25 (°C).
Appendix A – Modbus Reference
81