Modbus

The Modbus protocol was originally developed and published by Modicon at the beginning of the 80ies. The standard is primarily used in process automation. Because of its openness and simplicity, it has become a de-facto industry standard. The Modbus Organization has taken care of its further development and updates, it also provides all protocol-related documentation.

Modbus supports two different transmission modes:

  • Modbus serial
    supports communication via serial interfaces such as RS232, RS485
  • Modbus TCP/IP
    supports communication based on TCP/IP technologies

Modbus serial supports two different transmission modes:

  • Modbus RTU
    uses binary data encoding
  • Modbus ASCII
    uses ASCII code for encoding data in readable character strings

Today, only Modbus RTU communication is still in practical use.

Modbus applies the master/slave principle, where one master can communicate with one or several slaves. A slave can only respond to explicit requests (polls) by the master.

Modbus supports only binary and 16-bit values, which are read in blocks by the master, neither quality identifiers nor time stamps can be used.

ISO/OSI Model

7 Application Layer Modbus Application Layer
6 Presentation Layer n/a
5 Session Layer n/a
4 Transport Layer n/aTCP (RFC 793)
3 Network Layer n/aIP (RFC 791)
2 Link Layer n/aIP (RFC 791)
1 Physical Layer RTU (binary encoding)
ASCII (ASCII encoding)
RS232 (V.24), RS485
Ethernet (IEEE 802.3)

Supported Information Types

Control Direction
  • Single Command
  • Digital setpoint [16 bit]
Monitoring Direction
  • Single indication [1 Bit]
  • Measured value [16 bit]

Implemented Protocol Stacks

Modbus, Master

Modbus, Slave

Modbus TCP/IP, Master

Modbus TCP/IP, Slave

Applicable Products

  • ipConvLite
    ipConvLite

    inexpensive protocol converter for standardized application

  • ipConvOPC
    ipConvOPC

    Softwarepackage for conversion between OPC DA 3.0 Server and standard protocols

  • ipConvPBS
    ipConvPBS

    Universal protocol converter with integrated PROFIBUS-DP, slave interface

  • ipConvPBM
    ipConvPBM

    Universal protocol converter with integrated PROFIBUS-DP, master interface

  • ipConvPNM
    ipConvPNM

    Universal protocol converter with integrated PROFINET-IO, master interface

    Available soon !
  • ipConvPNS
    ipConvPNS

    Universal protocol converter with integrated PROFINET-IO, slave interface

  • ipConv
    ipConv

    Universal protocol converter for highest degree of flexibility

References

  • ELIA
    ELIA, Belgium

    Products: ipConv
    Protocol Stacks: Modbus TCP/IP, Master IEC 60870-5-104, Slave Telegyr 065, Master Telegyr 102, Master Telegyr 809, Master Tracec 32, 62, 92, 92P, 122, 130 & 142 Master

  • Storebælt
    Storebælt, Denmark

    Products: ipConv
    Protocol Stacks: IEC 60870-5-104, Master IEC 60870-5-104, Slave Simatic TDC, Master Modbus TCP/IP, Master

  • HVDC
    HVDC, New Zealand

    Products: ipConv ipConvLite
    Protocol Stacks: DNP V3.00, Slave DNP V3.00, Master TASE.2, Server TASE.2, Client Modbus, Master Simatic TDC, Master

  • Mainova Communication Hub
    Mainova Communication Hub, Germany

    Products: ipConv
    Protocol Stacks: OPC DAXML 1.01, Server IEC 60870-5-104, Slave IEC 60870-5-101, Master Modbus, Master SEAB 1F, Master

  • Power Plant Boxberg
    Power Plant Boxberg, Germany

    Products: ipConvLite ipConvPM
    Protocol Stacks: IEC 60870-5-104, Slave IEC 60870-5-104, Master Modbus, Slave Profibus-DP, Master

  • Neptune RTS
    Neptune RTS, USA

    Products: ipConv
    Protocol Stacks: DNP V3.00, Slave Simatic TDC, Master Modbus, Master CDC Type I, Slave

  • Metro Istanbul
    Metro Istanbul, Turkey

    Products: ipConvLite
    Protocol Stacks: Modbus, Master IEC 60870-5-104, Slave

  • Nordsee One
    Nordsee One, Germany

    Products: ipConv
    Protocol Stacks: Modbus, Master IEC 60870-5-104, Slave IEC 60870-5-101, Slave IEC 61850, Client IEC 61850, Server OPC UA 1.02, Server SNMP, Client

  • DUBAL21
    DUBAL21, United Arab Emirates

    Products: ipConvLite
    Protocol Stacks: DNP V3.00, Slave Modbus TCP/IP, Master

  • PEMEX, Madero
    PEMEX, Madero, Mexico

    Products: ipConv
    Protocol Stacks: DNP V3.00, Slave Harris-5000/6000, Slave Modbus, Master