Modbus (ASCII/RTU) Communication Standard

Modbus

Modbus is a serial communications protocol originally published by Modicon (now Schneider Electric)

Modbus is an open data communication protocol

Modbus is open structure, flexible, independent of the physical layer

Modbus is supplied by many SCADA and HMI software

Modbus is 2 serial transmission modes

ASCII - 10 bits

RTU (Binary) - 11 bits

Modbus is Communication interface

RS-232/485

Ethernet(TCP/IP)

Application

Used to establish master-slave/client-server communication between intelligent devices

Openly published and royalty-free

Modbus enables communication between many (approximately 247) devices connected to the same network

Communication between MODBUS devices

MODBUS devices communicate using a master-slave technique in which only one device (the master) can initiate transactions (called queries).

The other devices (slaves) respond by supplying the requested data to the master

A slave is any peripheral device (I/O transducer, valve, network or other measuring device), which processes information and sends its output to the master .

Masters can address individual slaves, or can initiate a broadcast message to all slaves.