The Modbus protocol was developed in 1979 by Modicon. It is used to establish master / slave (or client / server) communication between programmable controllers. It has become an industry standard method for the transfer of discrete I/O, analog I/O and register data between industrial control and monitoring devices.

Modbus RTU and Modbus ASCII are used in serial communication. Modbus RTU mode is the most common implementation and makes use of a compact, binary representation of the data. Modbus ASCII uses ASCII characters for protocol communication.

Thermal Mass Flow Controller with Modbus interface
Thermal Mass Flow Controller with Modbus interface


  • Baud rates from 9,6 kBaud up to 115,2 kBaud
  • +15 Vdc or +24 Vdc supply voltage
  • RTU/ASCII transmission mode with broadcast support (basic slave implementation class)
  • RS485 2W-cabling (vendor specific RJ45 (laboratory) connector or 5-pin M12 (industrial) connector)
  • station-address and Baud rate setting by Modbus or using configuration tool via RS232
  • option: galvanic isolation up to 500 V (for data lines)
  • connection of max. 247 instruments to 1 bus (without repeater)
  • max. bus length: 600 metres

Modbus RTU/ASCII system example

Modbus downloads

Modbus RTU/ASCII accessories
Modbus manual