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Communication protocols
Modbus TCP
Modbus TCP protocol allows for measured values from device to the 3
rd
party
SCADA software. Modbus TCP server supports two connections (sockets)
simultaneously. Default TCP port is 502. Modbus device address (Unit
Identifier) can be arbitrary. Modbus write command is not supported. Brief
description and example in Python language is available at About / Library
section of webpages. Detail description of the Modbus protocol is free to
download at
Supported Modbus commands (functions):
Command
Code
Description
Read Holding Register(s)
0x03
Reads 16-bit register(s)
Read Input Register(s)
0x04
Reads 16-bit register(s)
Table with Modbus registers. Depending on used communication library it
may to be required insert register number(s). Number of the register is an
address of register plus one (e.g. register with number 0x9C41 have the
Modbus address 0x9C40). Inside Modbus TCP frames are physically send
address.
Variable
Address
[HEX]
Address
[DEC]
Type
Device identification
Serial number
(device serial number have 8 digits which are split
into four Modbus registers)
0x9C22
39970
BCD
0x9C23
39971
BCD
0x9C24
39972
BCD
0x9C25
39973
BCD
Device type
0x9C26
39974
HEX
Device states
Internal acoustic signalisation
0x9C27
39975
INT
Optical LED signalisation
0x9C28
39976
INT
RSSI value
0x9C29
39977
INT
Configuration error
0x9C2A
39978
INT
System alarm - measurement error
0x9C2B
39979
INT
Low voltage of RTC battery
0x9C2C
39980
INT
Measured values