What is UART Communication? Block Diagram

What is UART?

UART or Universal Asynchronous Receiver Transmitter is a communication system where two UART devices can directly communicate to each other. It is dedicated hardware that helps to transmit data in a serial communication system. So, basically, it is a hardware communication protocol. The hardware of the UART system is a circuit that is generally integrated into an IC such as Microcontroller IC. The main purpose of UART is to transmit and receive data. It works on the physical level.

How does UART Works?

The working principle of the UART is very simple. In a communication system, two UART is required. One is connected to the device which will send the data, it may be a computer means CPU. Another UART is connected to the device that will receive the data. So we can mark the sending computer as computer 1 and the transmitter UART as UART1. Also, we can mark the receiving UART as UART2 and receiving computer as computer 2.

Now, when computer 1 wants to send data to computer 2. At first, computer 1 will send the data in parallel form to the UART 1. The UART 1 will convert the data into serial form and transmit or send to the receiver UART 2. The UART 2 again converts the serial data into parallel form and provides it to computer 2.

Now, computer 2 wants to send data to computer 1. So computer 2 will send the data to the UART 2 in form of parallel. The UART 2 will convert the parallel data into serial form and send it to UART1. The UART 1 will receive data in serial form and convert it into parallel form. After it will send to computer 1.

UART Block Diagram

Here, you can see the block diagram of UART that will help you to understand the working principle of UART.

UART Block Diagram, block diagram of UART Communication System

Here, you can see both of the UARTs are have transmitted and receiver circuits. So the transmitter of UART 1 will communicate with the receiver of the UART 2 while the receiver of UART 1 will communicate with the transmitter of UART 2.

Data Transmission in UART Communication

In the UART communication system, the data is transmitted in form of packets. Each of the packets consists of a start bit, stop bit, data frame, and a parity bit.

Start Bit

It is used to start the communication or data transmission. In the normal condition, when the system does not transmit any data, the transmission line is held at a high voltage level. But when it transmits data the voltage level is pulled down from the high voltage to a low voltage level for one(1) clock cycle. So the receiving UART detects high to low voltage transition and starts reading data in the data frame.

Data Frame

It consists of the actual data being transferred. The data in the data frame can be five(5) bit to Eight(8) bits long when a parity bit is used, When the parity bit is not used then the length of the data can be up to nine(9) bits. It can be also called as a data packet.


The parity number is used to make sure if any changes or data loss happens during the transmission. It is done by indicating even or odd numbers. When the parity bit is 1 that means the total of the high logic bit or 1 is odd and when the parity bit is 0 that means the total of the high logic bit or 1 is even. When the parity bit is 1 but the total of high bits is not odd then the system will detect there is an error.

Stop Bits

At the end of the data transmission, the sending UART drives the data transmission line from a low voltage to high voltage for one(1) or two(2) bits duration. So, it can help to understand the separation between two different data frame.

UART Examples, Uses, Applications, Advantages

You can see examples of UART in Bluetooth Modules, GPS Receiver, RFID applications. The main advantages of UART communication are simpler than others, needs only two lines, works on the physical level, etc.

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What is UART Communication? Block Diagram What is UART Communication? Block Diagram Reviewed by Author on 1/25/2022 Rating: 5

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