Modbus is a Master-Slave protocol which was developed in 1979 and has established itself as the standard in building automation. As an open protocol it is used extensively in industry and building automation. Modbus is standardized in the international IEC 61158 series of standards and is maintained by the Modbus organization.

There are different protocol versions:

  1. Modbus RTU - for the serial interface RS-232 (device-to-device connection, max. 15m cable length) and RS-485 (max. 32 participants, max. 1200m cable length, depending on the transmission rate) 
  2. Modbus ASCII (is similar to Modbus RTU to parameterize, rarely seen and is not supported by us)
  3. Modbus TCP - for Ethernet

Transfer functions:

The following standards are available for transmission:

Internal memory areaObject type Access modeRemark
Input StatusSingle bits Read only Data coming, for example, from the I/O of a device
Output/Coil Status Single bits Read / Write Bit information that can be changed by the user program
Input Register 16 bit words Read only Values that come, for example, from the analog I/O of a device.
Holding register 16 bit words Read / Write Internal word variables, changeable by the user program


This makes it easy and safe to exchange data (states or values such as temperatures, brightness, etc.) with other systems.

In the world of ISYGLT, Modbus is the ideal protocol for data exchange with systems such as heating / air conditioning / ventilation systems and other building automation servers, or with media controls such as Crestron or AMX.



  • Modbus TCP - Client


  • Modbus TCP Master
  • Modbus RTU Master
    If the IPMS server is supplied together with our Mini-PC, Modbus RTU can be operated either via RS-232 or RS-485.