Vaisala Indigo500 Series - A.5 Modbus Communication Examples

A.5 Modbus communication examples
Reading RH value from HMP4 probe connected to the
transmitter as Probe 1
The values returned by the device dier depending on the ambient conditions.
Your device might not return exactly the same values.
Request Response
Bytes in the frame
(hexadecimal)
Description Bytes in the frame
(hexadecimal)
Description
00
hex
Transaction identifier 00
hex
Transaction identifier
01
hex
01
hex
00
hex
Protocol identifier 00
hex
Protocol identifier
00
hex
00
hex
00
hex
Length (6) 00
hex
Length (7)
06
hex
07
hex
F1
hex
Unit identifier
(probe 1)
F1
hex
Unit identifier
(probe 1)
03
hex
Function (Read
Holding Registers)
03
hex
Function (Read
Holding Registers)
00
hex
Register address 04
hex
Number of data bytes
00
hex
7A
hex
Value of first register
(least significant
word)
00
hex
Number of 16-bit
registers to read (2)
E1
hex
02
hex
41
hex
Value of second
register (most
significant word)
F4
hex
Communication description
Transaction identifier Any number identifying the response and the corresponding
request on a Modbus TCP/IP transaction
Protocol identifier 0 (Modbus Protocol) as specified for Modbus TCP/IP
Length Number of remaining bytes in the frame starting from the unit
identifier
Appendix A – Modbus reference
117