Wired Communication Protocols

Wired Communication implies transmission of data from the transmitter to the receiver end point over a wired physical medium. Examples of wired communication includes Telephone lines and Television transmission system. It may use devices like ethernet, RS-232 or RS-485 cables or Universal Serial Bus (USB) for data transmission. It is advantageous to use Wired Communication technologies where the data transmission speed matters and not the distance of the transmission.

Internet of Things or IoT is a broad area where it employs a mix of Wired and Wireless form of communication. The choice of the communication type in an IoT application depends on many deciding factors like power consumption, data transmission speed, network range, data security etc.

IoT solution mostly utilises Wireless Communication network. However, at some point most of these networks become wired and hence IoT uses a hybrid of both the types of networks. Therefore, it is important that we know about the technologies available in Wired Communication too. The Wired Communication works similar as the Wireless counterpart except that the channel where the signal gets transmitted and received is “wired” like optical fibre, co-axial cable or ethernet.

Wired communication block diagram
Figure. Block Diagram of Wired communication

Wired Communication Protocols

The wired communication can be internal as well as external. The internal protocols imply communication from a microcontroller to another peripheral on the same silicon board and these are:

  • I2C
  • SPI

The external protocols are communication from one device to another which are physically separate from each other. The external protocols are:

  • Ethernet
  • RS-232
  • RS-485
  • USB

Let us discuss these protocols one by one

Internal Communication Protocols

• I2C – I2C or Inter Integrated Circuit bus was first developed by Philips in 1980. It is an internal communication protocol that uses only two wire for communication. SCL for clock and SDA for data transmission. Communication is always initiated by master and appropriate slave devices can respond to the message from the master. Communication is half-duplex, meaning that the device can either send or receive messages at a given instance. It comes in three variants of speed: slow (under 100 kbps), Fast (400 kbps) and High speed (3.4 Mbps).

• SPI – SPI or Serial Peripheral Interface Bus is a serial synchronous communication developed by Motorola in 1980s. It uses four wires for communication – SCLK (Serial Clock), MOSI (Master Output Slave Input), MISO (Master Input Slave Output) and SS (Slave Select). Communication is full-duplex i.e. the devices can transmit and receive simultaneously. It is the SS or chip select line which decides which slave will respond to the master.

External Communication Protocols

• Ethernet – It is a communication protocol to link and connect computing devices to form a Local Area Network or LAN. It was first developed by the Xerox Palo Alto Research Centres (PARC) in the mid-1970s. Every device with Ethernet connectivity will have a Network Interface Card (NIC) which will store the device’s unique physical address or identifier. This physical address is also called MAC (Media Access Control) address. Most of the business and institutional organisations employ Ethernet to build up their LAN network. It comes in various speed variants like the Standard Ethernet (10 Mbps), Fast Ethernet (100 Mbps), Gigabit Ethernet (1000 Mbps) and 10 Gigabit Ethernet (10 Gbps).

• RS-232 – Recommended Standard 232 is a serial communication standard developed by the Electronic Industry Association (EIA) and Telecommunication Industry Association (TIA). The standard defines the electrical signals and their timings. It serialises data to be sent to modem and de-serialises them back received from the modem. It has simple wirings and uses half-duplex master slave operation. Its current version is TIA-232-F.

• RS-485 – It is the improved version of the RS-232 which can connect up to 10 to 32 devices simultaneously. It has good noise immunity and thus is the preferred choice of serial communication in industries. It can have a cable whose length may extend up to 4000 feet.

• UART / USART – UART stands for Universal Asynchronous Receiver Transmitter and USART stands for Universal Synchronous Asynchronous Receiver Transmitter. UART is the name of the hardware used in RS-232. It is asynchronous as it does not require any clock for synchronisation. It can be used for inexpensive type of communication. USART uses clock for synchronisation in case of Synchronous communication. It can also work in asynchronous mode. It is full-duplex type of serial communication.

• USB Universal Serial Bus is a serial communication protocol for connecting devices, usually a computer. Nowadays it can be used for connecting other devices also which have USB ports like gaming consoles, mobile phones, Set-top box etc. The latest version USB 3.0 gives a speed of 5 Gbps and provides full-duplex mode of communication.


Anupama kumari

M.Tech (VLSI Design and Embedded system)

BS Abdur Rahman University

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