Modbus

Added in version 4.4.

NetXMS can collect data via the Modbus-TCP protocol. Data collection is performed by the NetXMS server or by NetXMS agents operating in proxy mode.

To enable agent operation as a Modbus proxy, add EnableModbusProxy=yes to the agent configuration file and restart the agent.

The metric for Modbus data collection items has a special format denoting the type of Modbus unit id, register type, register address and the way how obtained data should be interpreted:

[[unit-id:]register-type:]register-address[|conversion]

Metric component

Description

unit-id

Modbus unit ID. Optional, if used, should be specified without [ ]. To use it, register-type should also be provided.

register-type

Type of Modbus register. Optional, if not specified, hold will be used. Should be specified without [ ] if used. Supports following values:

  • coil - Coil

  • discrete - Discrete Input

  • hold - Holding Register

  • input - Input Register

register-address

Address of Modbus register. Can be provided as decimal number or hexadecimal number prefixed by 0x.

conversion

Conversion of Modbus data. Optional, if not specified, uint16 will be used. Should be specified without [ ] if used. Affects the number of Modbus registers being read and how read data is interpreted:

  • int16 - 16 bit signed integer

  • uint16 - 16 bit unsigned integer

  • int32 - 32 bit signed integer (will read 2 registers)

  • uint32 - 32 bit unsigned integer (will read 2 registers)

  • int64 - 64 bit signed integer (will read 4 registers)

  • uint64 - 64 bit unsigned integer (will read 4 registers)

  • float - same as float-abcd

  • float-abcd - 4 byte floating point number, ABCD byte order

  • float-cdab - 4 byte floating point number, CDAB byte order

  • float-badc - 4 byte floating point number, BADC byte order

  • float-dcba - 4 byte floating point number, DCBA byte order

  • double - same as double-be

  • double-be - 8 byte floating point number, big endian byte order

  • double-le - 8 byte floating point number, little endian byte order

  • string-N - string of N characters (will read (N + 1) / 2 registers)

  • string-N-CP - string of N characters encoded using codepage CP (will read (N + 1) / 2 registers)

Modbus metric examples

0x2A
Read holding register at address 2A hexadecimal (42 decimal), interpret as uint16.
input:8
Read input register at address 8 decimal, interpret as uint16.
10|int16
Read holding register at address 10 decimal, interpret as int16.
input:55|float
Read two input registers starting from 55 decimal, interpret as float with ABCD byte order.