What is the relationship between Modbus and RS485?

RS-485

RS-485 is a physical interface, in simple terms, hardware.

It only requires two communication lines, which enables data transmission between two or more devices.

This type of data transmission connection is a half duplex communication method. At a certain moment, a device can only send or receive data.

After the hardware communication interface is established, a data protocol needs to be agreed upon between the instruments for data transmission, so that the receiving end can parse the received data. This is the concept of "protocol".

There is a unified standard protocol format for communication protocols, such as the "ModBus" protocol. The standard protocol content is comprehensive and includes a lot of content, but it is not easy to understand. As a result, some manufacturers have customized a protocol that is simple and practical, which is called a "custom protocol".

RS-485 bus has been widely used in various fields such as smart homes, security monitoring, intelligent transportation, intelligent buildings, computer room monitoring, industrial automation, etc. due to its low cost and simple design. The RS-485 bus wiring is relatively simple, but there are some corresponding matters that must be paid attention to, otherwise it may easily lead to communication failure.

Modbus

Modbus is one of the communication protocols, just like Chinese and English, it is a language of communication, a language of communication between machines.

So before communication, there must be a communication bridge, which is the transmission medium RS-485 or RS-232 and other electrical rules.

The same protocol can use different transmission media, such as RS-485 or RS-232

The Modbus protocol is divided into three modes: Modbus RTU, Modbus ASCII, and later developed Modbus TCP.

The first two types of physical hardware interfaces used are both serial communication ports (RS-232, RS-485, RS-422). Modbus TCP, on the other hand, is designed to keep up with the current trend of world development and can be connected and transmitted through Ethernet or the Internet. So it is also called Modbus TCP mode, and the hardware interface of this mode is the Ethernet port, which is the network port commonly used on our computers.

So, RS485 is the hardware, Modbus is the communication language, and they can collaborate to implement international standard protocols for device communication.