Arduino RS-485 Modbus Cable

Modbus Industrial IoT Gateway Cable


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What is a Modbus Industrial IoT Gateway


Modbus Industrial IoT Gateway is a protocol converter that supports Modbus interface (RS232/485) and Modbus TCP.


With the function of Modbus TCP to Modbus RTU, it is an industrial gateway device that supports multi-protocol conversion, and also supports the conversion of private protocols of various manufacturers. Users can easily realize the connection between industrial IoT gateway Modbus Ethernet devices and Modbus serial devices.


At the same time, Jixun Industrial IoT Gateway also supports edge computing and face recognition functions, which can help users filter unnecessary data, solve the problems of too large transmission data and too much bandwidth required, and can also help enterprise management and video in-depth analysis functions. It can help enterprises analyze abnormal behaviors in the area and report to the police in time.


Industrial IoT Gateway is a bus protocol for industrial fields. The Modbus communication protocol industrial gateway is commonly used in the communication of third-party devices, such as DCS reading PLC data, smart meters (flow meters, analyzers and other equipment) data.


Usually divided into 3 types of data protocols, Modbus RTU and Modbus TCP/IP, Modbus ASCII.


Introduction of three communication protocols of Modbus gateway


The Modbus gateway protocol is divided into three communication modes: Modbus RTU, Modbus ASCII and Modbus TCP.


The communication format of Modbus TCP is similar to that of Modbus RTU, the difference is that Modbus RTU has a two-byte CRC check, while Modbus TCP does not.


The communication format of Modbus ASCII and Modbus RTU is actually to split each byte (for example: 27H) of Modbus RTU into two bytes, the upper four bits (2) and the lower four bits (7), and use the ASCII code. Show (32 37), and then add the start character and end character to the frame respectively. Of course, the verification methods of Modbus RTU and Modbus ASCII are different, which are not introduced here, so the same Modbus RTU mode and Modbus ASCII mode are displayed. Out, although there is a big difference in length, but the actual meaning is the same.


In different fields, the industrial IoT gateway can not only be used as a terminal for data transmission, but also can be used as a regional device controller to control, such as: street light on and off, monitoring, flower garden watering time and other equipment control, becoming the city's intelligence control center.


Analysis of Arduino UNO to realize RS-485 Modbus serial communication scheme


Arduino acts as a MODBUS master (Master) to communicate with a MODBUS slave (Slave).

In this article, a computer with MODBUS Slave Software installed will be used as a MODBUS slave. So, let's start with a brief introduction to RS-485 and Modbus.


RS-485 serial communication


RS-485 is an asynchronous serial communication protocol that does not require a clock.

It uses a technique called differential signaling to transmit binary data from one device to another.

It provides half-duplex communication when two wires are used, while full duplex requires 4 wires.

The RS-485 module can be connected to any microcontroller with a serial port.

When using an RS-485 module with a microcontroller, a Maxim MAX485 based 5V MAX485 TTL to RS485 module is required as it allows serial communication over long distances of 1200 meters.

It is bi-directional and half-duplex, the data transfer rate is 2.5 Mbps, and the module requires a voltage of 5V.

USB to RS485 converter adapter module, supports WIN7, XP, Linux, Mac OS, and provides an easy-to-use RS485 interface by using the COM port in the computer.

The module is a plug and play device. Without the command structure, anything sent to the virtual COM port is automatically converted to RS485 and vice versa. The module is fully powered by the USB bus. Therefore, no external power supply is required to operate.

It appears as a serial/COM port and can be accessed from an application or hyperterminal. This converter provides half-duplex RS-485 communication. Baud rates range from 75 bps to 115200 bps, up to 6 Mbps.

Modbus Slave software

The Modbus Slave application receives values ​​from any Modbus master device by using the serial communication port. It is a data communication test software

SlaveID: Each slave in the network is assigned a unique unit address from 1 to 127. When the master requests data, the first byte it sends is the slave address.

Modbus registers:

Discrete Output Coil: It is a 1-bit register that controls the discrete output and can be read or written. Their register numbers are (1 to 9999).

Discrete Input: It is a 1-bit register that is used as an input and can only be read. They have registration numbers (10001 to 19999).

Input Register: 16-bit register for input, read only. Their register numbers are (30001 to 39999).

Holding Register: It is a 16-bit register that can be read and written. Their register numbers are (40001 to 49999).

Required components

● Arduino UNO development board

● MAX-485 TTL to RS-485 conversion module

● USB to RS-485 conversion module

● 1602 LCD display

● Modbus Slave

RS-485 serial communication Cable

Modbus Industrial IoT Gateway Cable

Arduino RS-485 Modbus serial communication Cable


Arduino RS-485 Modbus CableRS-485 serial communication CableModbus Industrial IoT Gateway Cable

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