Communication Protocols

What are the different types of Communication Protocols?

What are communication protocols?

Communication protocols are the set of rules that allow two or more electronic devices to connect and exchange data with each other.

They have proper descriptions of digital message formats and rules.

They are important for digital and analog communications to take place.


Types of communication protocols

Communication protocols are of two types. They are:

  1. Inter System Protocol
  2. Intra System Protocol


Inter System Protocol

It is used for communication between two different devices. Say, for example, communication between a computer and a microcontroller circuit.

communication protocol

Different categories of Inter System protocols are:

1. UART Protocol – Universal Asynchronous Transmitter and Receiver
  • It is a serial communication protocol, with two wired protocols.
  • The data cable signal lines are labeled as Rx(receiver) and Tx(transmitter). It is a Half-Duplex protocol. (i.e., it can send and receive data but not at the same time)
  • UART takes bytes of data and sequentially sends the individual bits. It has one start bit, 8-bit data, and one stop bit.
2. USART Protocol – Universal Synchronous and Asynchronous Transmitter and Receiver
  • It is a serial communication protocol, with two wired protocols.
  • The data cable signal lines are labeled as Rx(receiver) and Tx(transmitter). It is a Full-Duplex protocol. (i.e., it can send and receive data at the same time by different baud rates)
3. USB Protocol – Universal Serial Bus
  • It is a serial communication protocol, with two wired protocols.
  • The data cable lines are labeled D+ and D-.
  • It is used to send data serially to the host and peripheral devices.
  • There are different modes of transfer-slow speed mode(10kbps to 100kbps), full speed mode(500kbps to 10mbps), and high-speed mode(2mbps to 400 Mbps).
  • The maximum cable length is 4 meters. Examples: mouse, keyboard, etc.


Intra System Protocol

It is used to communicate the two devices within the circuit board. They reduce the circuit complexity, power consumption, and cost. It is very secure to access data.

communication protocol

Different categories of Inter System protocols are:

1. I2C Protocol – Inter-Integrated Circuit Protocol
  • It is a master-slave communication protocol.
  • It has two wires SDA (Serial data line) and SCL (Serial clock line) for carrying information between devices.
  • SDA and SCA are bidirectional.
2. SPI Protocol – Serial Peripheral Interface Protocol
  • It is a serial communication protocol developed by Motorola.
  • It is also called a 4-wire protocol. It has four wires-MOSI, MISO, SS, and SCLK.
  • It is used to communicate master-slave devices.
  • It is a full duplex communication protocol. It is not limited to 8-bit words in data transferring.
3. CAN Protocol – Controller Area Network Protocol
  • It is a serial communication protocol.
  • It has two wires Can High (H+) and CAN Low (H-).
  • It is based on a network-oriented transmission protocol.


Industrial Instrumentation Protocols

In the field of process automation, the following are the most commonly used communication protocols:

1. RS-232 Communication Protocol

  • RS-232 is an asynchronous communication method.
  • It uses a binary system to transmit data in ASCII format.
  • PLCs serial port is used for transmission/reception of data. It works by sending/ receiving voltage.
  • Normally 1 bit (a high bit) is represented by a voltage -12 V. And the 0 bit(low bit) is represented by a voltage +12 V.


2. RS-485 Communication Protocol

  • RS-485 is a multi-drop and two-wire type of communication that allows us to communicate with multiple devices at the same time.
  • The number of devices that can be connected: 32 devices.
  • Maximum distance: 1200 meters(end to end)
  • Many PLCs allow connecting up to 128 slave nodes. By using repeaters number of devices and nodes can be extended.
  • It can be used as a 2-wire or 4-wire network. The 4-wire network would be bidirectional and a 2-wire network would be unidirectional.


3. Ethernet(TCP/IP) Communication Protocol

  • Ethernet is the local area network and devices that were defined under IEEE.
  • TCP/IP stands for Transfer Control Protocol/Internet Protocol.
  • The network nodes are of two types: Data Terminal Equipment (DTE) and Data Communication Equipment (DCE).
  • DTE are devices that generate/ are a destination of data. Examples: PCs, workstations, print servers, etc.
  • DCEs are intermediate devices that receive and retransmit frames within a network. Examples: routers, switches, repeaters, etc.
  • It uses IP(Inter-Network or internet protocol) for routing.
  • Baud rate: 100 Mbps.
  • Length: Few km
  • Nodes: 255

communication protocol


4. HART(Highway Addressable Remote Transducer) Protocol

  • HART is a master-slave protocol.
  • It can be used in many modes like point-to-point or multidrop for communicating information to/from smart field instruments and central control/monitoring systems.
  • It provides up to two maters-primary and secondary. So, secondary masters like handheld communicators are to be used without interfering with communications with the primary master, i.e., control/monitoring system.
  • Maximum devices: 15 in multidrop
  • Network Topology: point-to-point, multidrop, wireless mesh
  • There are two simultaneous communication channels: 4-20mA analog signal and a digital signal.
  • The signal frequencies of bit values 0 and 1 are 2200 and 1200Hz respectively.

communication protocol


5. Modbus RTU

  • Modbus RTU is an open serial protocol derived from Master-slave architecture originally developed by Modicon (now Schneider Electric).
  • RTU stands for Remote Terminal Unit.
  • It is widely accepted due to its ease of use and reliability.
  • Modbus RTU messages are simple 16-bit structures with CRC (Cyclic-Redundant Checksum). The simplicity of these messages is to ensure reliability.

communication protocol


6. Profibus

  • Profibus makes use of three separate layers of an OSI model.
  • It first describes the Application Layer. Here, multiple versions of Profibus handle different types of messaging at the application layer.
  • Type of messaging supported by PROFIBUS- cyclic and acyclic data exchange, diagnosis, alarm handling, and isochronous messaging.
  • It does not define layers three to six.
  • It then defines Data Link Layer and Physical Layer(i.e., layers 1 and 2). The data link layer is completed by a Field Bus Data Link(FDL). FDL combines, master-slave and token passing.
  • In the physical Layer, PROFIBUS systems can have three types of media. The first one is a standard twisted pair wiring system(RS485). Secondly, a fiber optic transmission, and thirdly, a safety-enhanced system called Manchester Bus Power (MBP) for situations where the chemical environment is prone to explosion.
  • Network Topology: It uses the Bus Topology. In this, a central line, or bus, is wired throughout the system. Devices will be attached to the main bus.
  • Profibus DP(Decentralized Periphery) device is any peripheral device that has information and sends its output to the master. The DP device forms a passive station on the network and can only acknowledge received messages or send response messages to the master upon request.
  • All DP devices have the same priority and all network communication originates from a master.
  • Maximum Frame Size: 244 bytes
  • A maximum number of nodes: 126 with 32 maximum per slave.
  • Baud rate: 5-12 Mbps.
  • Length: 15 km.

communication protocol


7. ProfiNet

  • It is an Industrial Ethernet.
  • It is faster with more bandwidth and larger messages.
  • It is a newer, Ethernet-based industrial communication protocol.
  • The physical interface used for Profinet is a standard RJ-45 Ethernet Jack. The cable is easily recognized by its green color.
  • Profibus devices have three different types of addresses: IP address, MAC address, and Device name.
  • All Ethernet devices use IP addresses and MAC addresses but the Device Name is unique to Profinet devices.
  • Due to its higher speed and greater flexibility, Profinet is becoming the preferred communications protocol for industrial applications.

communication protocol


8. Interbus

  • It is a serial bus system that transmits data between control systems like PLCs, PCs, Robot controllers, etc.
  • It is one of the leading field bus systems in the automation industry and is fully standardized according to European Standard.
  • They have spatially distributed I/O module that is connected to sensors and actuators. Example- temperature sensors, etc.
  • Network Topology: Ring Topology(all devices are actively integrated into a closed transmission path)

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