Modbus Protocol

Modbus is a serial communications protocol published by Modicon in 1979 for use with its programmable logic controllers (PLCs).

Modbus is often used to connect a supervisory computer with a remote terminal unit (RTU) in supervisory control and data acquisition (SCADA) systems.

Versions of the Modbus protocol exist for serial port and for Ethernet.

For serial connections, two variants exist, with different representations of numerical data and slightly different protocol details. Modbus RTU is a compact, binary representation of the data. Modbus ASCII is human readable, and more verbose. Both of these variants use serial communication. The RTU format follows the commands/data with a cyclic redundancy check checksum, while the ASCII format uses a longitudinal redundancy check checksum. Nodes configured for the RTU variant will not communicate with nodes set for ASCII, and the reverse.

For connections over TCP/IP, the more recent variant Modbus/TCP exists. It does not require a checksum calculation.

I have applied tcp/ip modbus protocol for Koyo PLC to communicate with Daqfactory SCADA. It has done very well.


86 thoughts on “Modbus Protocol”

  1. @wigati. betul sekali modbus penghubung antar hardware atau hardware dan viewer itu menurut pemahaman saya. kebetulan scada yang saya gunakan menggunakan modbus sehingga dalam penetuan plc saya selalu mempertimbangkan plc yang support modbus.

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  13. Modbus protocol (derived from the abbreviation 'Modicon Bus') was originally developed by Modicon (Schneider Automation) in the late 1970s. Modbus has many variants depending on the applications used. Modbus variant most commonly used:- Modbus RTU- Modbus ASCII- Modbus TCP- Modbus Plus

  14. whether this also requires a calculation for algorithm?I think to discuss the CRC calculation for the Modbus protocol. A two 8bit byte CRC code must be created and sent along with another byte of data you will send via com port.

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