Communications and protocols used in industrial automation
Industrial network protocols in industrial automation
29 June, 2020 by
Communications and protocols used in industrial automation
Boot & Work Corp. S.L., Berta Canet


1. Introduction

2. WiFi & Ethernet



5. Modbus protocols

    · Modbus RTU

    · Modbus TCP/IP

6. RS-232 & RS-485

7. I2C



In this post, you are going to learn the main industrial automation communications of our Industrial Shields' PLC Arduino and the types of industrial networking protocols list they work with.

Introduction of communications and protocols used in industrial automation

WiFi & Ethernet


In an industrial PLC controller Arduino, Wi-Fi uses multiple parts of the IEEE 802 protocol family and is designed to interwork seamlessly with its wired sibling Ethernet. Compatible devices can be networked via wireless access points to each other, as well as to wired devices and the Internet. The different versions of Wi-Fi are specified by various IEEE 802.11 protocol standards, which is an industrial wireless network protocol, with the different radio technologies determining radio bands, and the maximum ranges, and speeds that may be achieved. Wi-Fi most commonly uses the 2.4 gigahertz (120 mm) UHF and 5 gigahertz (60 mm) SHF ISM radio bands; these bands are subdivided into multiple channels. Channels can be shared between networks but only one transmitter can transmit locally on a channel at any time.


Ethernet is the most common technology working with the Local Area Networks (LANs) and Wide Area Networks (WANs). Ethernet communication uses the LAN protocol which is technically known as the IEEE 802.3 protocol. This industrial network protocol has evolved and improved over time to transfer data at the speed of one gigabit per second.

Our M-Duino family PLCs incorporate the W5500 IC integrated circuit. The W5500 is a hardwired TCP/IP embedded Ethernet controller that provides an easier Internet connection to the embedded systems. This chip allows users to have Internet connectivity in their applications by using the single chip in which  TCP/IP stack, 10/100 Ethernet MAC and PHY are embedded. The W5500 chip incorporates the 32Kb of internal memory buffer for processing Ethernet packets. With this chip, users can implement the Ethernet application by using Socket Programming. The SPI bus (Serial Peripheral Interface) is provided to facilitate the data transfer with the external microcontroller.

Ethernet uses different industrial protocols to communicate. Some of these are HTTP, HTTPS, MQTT and the Modbus protocols.


HTTP stands for Hypertext Transfer Protocol. When you enter http:// in your address bar in front of the domain, it tells the browser to connect via HTTP. HTTP uses TCP 


(Transmission Control Protocol), usually, through port 80, to send and receive data packets over the web.

HTTPS stands for Hypertext Transfer Protocol Secure (also known as HTTP over TLS or HTTP over SSL). When https:// is entered in the address bar opposite the domain, it tells the browser to connect via HTTPS. Generally, sites that operate over HTTPS will have a redirect in place, so even if you type http:// it will be redirected to deliver over a secured connection. HTTPS also uses TCP (Transmission Control Protocol) to send and receive data packets, but it does so through port 443, within a connection encrypted by Transport Layer Security (TLS).


MQTT (Message Queuing Telemetry Transport) is an open OASIS and ISO standard (ISO/IEC 20922) lightweight, a publish-subscribe network protocol that transports messages between devices. This automation communication protocol usually runs over TCP/IP; however, any network protocol that provides orderly, lossless, bi-directional connections can support MQTT. It is designed for connections with remote locations where a "small code footprint" is required or the network bandwidth is limited.

Modbus protocols

Modbus protocols

Modbus Protocol is a messaging structure developed by Modicon. It is used to establish Master-Slave/Client-Server communication between devices. Modbus has a lot of industrial automation protocol options. But the two most widely used are Modbus RTU (Remote Terminal Unit) and Modbus (TCP/IP) Transmission Control Protocol.

Modbus RTU & Modbus TCP/IP

Modbus RTU & Modbus TCP/IP
Modbus RTU mode is the most common implementation, but Modbus TCP/IP is gaining ground and ready to overcome it. Modbus is an open standard and is a widely used industrial network protocol in the industrial manufacturing environment. It is a common link that has been implemented by hundreds of vendors for integration into thousands of different manufacturing devices to transfer discrete/analog I/O and record data between control devices. A Modbus communication is always initiated by the master node to the slave node. The slave nodes will never transmit data without receiving a request from the master node or communicating with each other. The master node initiates only one MODBUS transaction at the same time.

Modbus RTU mode is the most common implementation, using binary coding and CRC error-checking. RTU Protocol is an efficient binary protocol in which each eight-bit (one byte) in a message contains two four-bit hexadecimal characters. Each message must be transmitted in a continuous stream. The format for each byte (11 bits) in RTU mode is Coding System: 8–bit binary, Bits per Byte: 1 start bit, 8 data bits, least significant bit sent first, 1 bit for parity completion, 1 stop bit. Modbus RTU packets are only intended to send data; they do not have the capability to send parameters, such as point name, resolution, units, etc.
RTU is extremely popular for industrial control networks as it has been around for a long time, and there is a lot of hardware and software that support it.

Modbus TCP/IP is basically the Modbus RTU protocol using the TCP interface in an Ethernet network. The Modbus data structure is defined using the application layer used in the TCP/IP protocol. The TCP, or transport protocol, is used to ensure data is received and sent correctly, and the IP is the address and routing information.
Essentially, the Modbus TCP/IP command is a Modbus RTU command included in an Ethernet TCP/IP wrapper. The benefit of using Modbus TCP/IP is using the existing Ethernet network equipment that is widely and available and cost-effective.

RS-232 & RS-485

RS-485, also known as TIA/EIA-485, is a standard defining the electrical characteristics of drivers and receivers for use in serial communications systems. Electrical signaling is balanced, and multipoint systems are supported. The standard is jointly published by the Telecommunications Industry Association and Electronic Industries Alliance (TIA/EIA). Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. Multiple receivers may be connected to such a network in a linear, multidrop bus. These characteristics make RS-485 useful in industrial control systems and similar applications.

Our Industrial Arduino-based PLCs include the integrated circuit MAX485. MAX485 is a low-power and slew-rate-limited transceiver used for RS-485 communication. It works at a single +5V power supply and the rated current is 300 μA. Adopting Half-Duplex communication to implement the function of converting the TTL level into RS-485 level, it can achieve a maximum transmission rate of 2.5Mbps. MAX485 transceiver draws supply current of between 120μA and 500μA under the unloaded or fully loaded conditions when the driver is disabled.

RS-485 Dip Switch configuration

RS-485 Dip Switch configuration

RS-232 (Recommended Standard 232) is a standard for serial communication transmission of data. It formally defines signals connecting between a DTE (Data Terminal Equipment) such as a computer terminal, and a DCE (Data Circuit-Terminating Equipment or Data Communication Equipment), such as a modem. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pinout of connectors. The current version of the standard is TIA-232-F Interface Between a DTE and a DCE Employing Serial Binary Data Interchange. The RS-232 standard had been commonly used in computer serial ports and is still widely used in industrial communication devices.

Our Industrial Arduino Based PLCs incorporate the integrated circuit MAX232. MAX232 converts signals from to TIA-232 (RS-232) serial port to signals suitable for use in TTL-compatible digital logic circuits. The MAX232 is a dual transmitter/dual receiver that is used to convert the RX, TX, CTS, RTS signals.

Industrial Arduino-based PLCs with I2C


I2C (Inter-Integrated Circuit), pronounced I-squared-C, is an asynchronous, multi-master, multi-slave, packet-switched, single-ended, serial computer bus. It is widely used for attaching lower-speed peripheral ICs to processors and microcontrollers in short-distance, intra-board communication.

Later on, the I2C was gradually adopted by other manufacturers until it became a market standard. The I2C bus requires only two cables for its operation, one for the clock signal (CLK) and the other for sending data (SDA), which is an advantage over the SPI bus. By cons, its operation is a little more complex, as well as the electronics necessary to implement it.

Industrial Arduino-based PLCs with GPRS


General Packet Radio Services (GPRS) is a packet-based industrial wireless communication service that promises data rates from 56 up to 114 Kbps and continuous connection to the Internet for mobile phone and computer users. GPRS is based on Global System for Mobile (GSM) communication and complements existing services such as circuit-switched cellular phone connections and the Short Message Service (SMS).

Equipment based on the Arduino technology designed for professional use. It also contains several communication ports which provide more flexibility and control. The GPRS/GSM family offers the possibility to expand up to 127 modules through I2C, which means that you can have until 7100 Inputs / Outputs in Master-Slave connections, additionally to sensors, etc.

The Industrial Arduino-based PLCs with GPRS is ideal for remote monitoring, data logging and remote access, diagnostics and control, using short text messages (SMS). You can adjust the messages to send from a device with static (text) or dynamic (text and values) content.

If you want to know more about our equipment, ask our team.

We will help you to find the device that best suits your needs.

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Communications and protocols used in industrial automation
Boot & Work Corp. S.L., Berta Canet
29 June, 2020
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