Modbus is the most commonly used industrial communication protocol for various devices & sensors to send and receive data. It is an request response protocol with master and slave devices connected to gether in a network, meaning master device will poll one or more slave devices and slave devices can only send data as a response to master device

Types of Modbus

Commonly there are three different types of modbus protocols operating in different OSI layer models but the underlying protocol is the same

• Modbus RTU (Most Common)
• Modbus TCP/IP
• Modbus ASCII
• Modbus Plus

| LAYERS | | | | | Application | MODBUS | MODBUS | MODBUS | | Presentation | | | | | Session | | | | | Transport | | | TCP/IP Messaging | | Network | | | Used | | Data Link | | | Used | | Physical | RS-232 / RS485 | HDLC | Ethernet | | PROTOCOLS | Modbus RTU | Modbus Plus | Modbus TCP |

As you can see above all types of Modbus uses same application layer with minor differences only for the error correction Modbus Plus is a peer to peer network protocol based on token passing communication and is a licensed protocol owned by Modicon so we wont discuss here in detail

Physical Connections

• Modbus RTU Uses RS-232 and RS-485 physical interface
• Modbus TCP Uses regular Ethernet physical interface

Modbus Data Communication Interface

Modbus is an serial communication protocol and uses registers for data access, there are 4 types of registers commonly used

• Discrete Output (Coil)
• Discrete Input
• Input Register
• Holding Register

Clofus can provide you support interfacing all your industrial sensors and devices to a IOT platform inorder to easily access your data, identify production bottlenecks and solve them effectively