UART: Universal Asynchronous Receiver/Transmitter
Published: 2023-04-10 10:35:44

Hi folks, I'm Basappa Hadapad employee of LUXOFT India. Here I would like to provide a brief knowledge about UART Protocol.
**Introduction** 
The UART (Universal Asynchronous Receiver/Transmitter) protocol is a commonly used communication protocol for serial communication between digital devices. It is a simple and reliable protocol that enables data transmission between devices through a single communication channel.
UART uses asynchronous communication, which means that data is sent without a clock signal. Instead, each data packet includes a start bit, data bits, an optional parity bit, and one or more stop bits. The start bit indicates the beginning of a new data packet, while the stop bit(s) signal the end of the packet.
To send data using UART, the transmitter sends a start bit followed by the data bits, and an optional parity bit (if used), and one or more stop bits. The receiver samples the data at a predefined time interval based on the baud rate, which is the rate at which data is transmitted.
One of the advantages of the UART protocol is its simplicity, which makes it easy to implement in hardware and software. UART also has low hardware requirements, as it only requires a single communication line and a few control lines. Additionally, UART is compatible with a wide range of devices and can be used in various applications, such as embedded systems, industrial automation, and communication between microcontrollers and peripherals.
However, the asynchronous nature of UART communication requires careful timing considerations. The receiver must sample the data at the correct time to ensure accurate reception, and any timing errors can result in data corruption. Furthermore, the limited error detection capabilities of UART may require additional error checking mechanisms to ensure data integrity.
Overall, the UART protocol is a fundamental and widely used communication protocol that enables devices to exchange data reliably and efficiently.

**Interfacing**

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In the UART protocol, data is transmitted between two devices using a transmitter and a receiver. The transmitter sends data one bit at a time to the receiver, which receives and reassembles the data into its original form. Here's a closer look at how the transmitter and receiver work:
1.	Transmitter(Tx)
2.	Receiver(Rx)

**Transmitter**: The UART transmitter typically consists of a shift register, a control circuit, and a clock signal. The shift register is used to store the data that is being transmitted, and the control circuit manages the transmission process. The clock signal is used to synchronize the transmission of data between the transmitter and the receiver.
When the transmitter is ready to send data, it first sends a start bit, which is a logical 0. This tells the receiver that data is coming. The transmitter then sends the data one bit at a time, starting with the least significant bit (LSB). The receiver uses the clock signal to synchronize its reception of the data. Once all the data bits have been transmitted, the transmitter sends a stop bit, which is a logical 1. This tells the receiver that the transmission is complete.
Receiver: The UART receiver typically consists of a shift register, a control circuit, and a clock signal. The shift register is used to store the received data, and the control circuit manages the reception process. The clock signal is used to synchronize the reception of data between the transmitter and the receiver.
When the receiver detects a start bit, it begins to receive the data bits, using the clock signal to synchronize the reception. Once all the data bits have been received, the receiver checks for any errors, such as a parity or checksum error. If the data is error-free, the receiver passes the data to the device or application that is using it. If an error is detected, the receiver can either request that the data be retransmitted or discard the data altogether.


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**Data Transmission** 


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In the UART protocol, data is transmitted serially, meaning that the bits are transmitted one at a time over a single communication line. Here's a closer look at how data transmission works in the UART protocol:
Start bit: The UART transmission begins with a start bit, which is a single bit with a value of 0. This signals the receiver that data is coming.
Data bits: After the start bit, the data bits are transmitted in the order of least significant bit (LSB) to most significant bit (MSB). Each data bit is represented as a logical 1 or 0.
Parity bit (optional): In some cases, a parity bit is transmitted after the data bits. The parity bit is used to check for errors in the transmission. There are two types of parity, even and odd. In even parity, the parity bit is set to 1 or 0 so that the total number of 1s in the data and parity bits is an even number. In odd parity, the parity bit is set so that the total number of 1s is an odd number.
Stop bit: The UART transmission ends with a stop bit, which is a single bit with a value of 1. This signals the receiver that the transmission is complete.
The length of the data frame in the UART transmission (including the start, data, and optional parity bits) can be configured to different sizes, typically 7 or 8 bits.
The UART transmission rate, also known as the baud rate, determines how quickly the data is transmitted. The baud rate is set by dividing the frequency of the UART clock by a prescaler value. Typical baud rates for UART transmissions range from a few hundred bits per second up to several megabits per second.
Overall, data transmission in the UART protocol is a simple, reliable, and widely used method of transmitting data between electronic devices.


**Steps of UART Transmission:**

**-Data preparation:** The data to be transmitted is first prepared by the sending device, typically a microcontroller or other embedded system. The data can be any type of information, such as sensor readings, commands, or status updates.
**-Start bit transmission:** The UART transmitter sends a start bit, which is a logical 0, to signal the start of the data transmission. The start bit is always followed by the data bits.
**-Data bit transmission:** The data bits are transmitted one at a time, starting with the least significant bit (LSB) and ending with the most significant bit (MSB). The number of data bits can vary, but it is typically 7 or 8 bits.
-Parity bit transmission (optional): In some cases, a parity bit is transmitted after the data bits to check for transmission errors. The parity bit can be set to even or odd, depending on the parity scheme used.
**-Stop bit transmission:** The UART transmitter sends one or more stop bits, which are always set to logical 1, to signal the end of the data transmission. The number of stop bits can vary, but it is typically one or two.

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![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/iaxzbiiw4s33xpcodfnf.png)




**Reception and error checking: **The UART receiver receives the data and checks for errors. If an error is detected, such as a parity error or a framing error, the receiver can either request that the data be retransmitted or discard the data altogether.

![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/c3lw0b4jgi7xr58zrphe.png)


**-Data processing:** If the data is error-free, the receiver passes it to the device or application that is using it. The data can be processed in a variety of ways, depending on the application, such as displaying it on a screen, storing it in memory, or using it to control a device.


![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/fay6kxfgqsbvzllrmd36.png)




**Applications :**
Serial Communication between Microcontrollers and **Peripherals:** In embedded systems, microcontrollers often communicate with peripherals such as sensors, motors, and displays using UART. The microcontroller sends commands and data to the peripherals, and the peripherals respond with status updates and sensor readings.
PC Communication with External Devices: Many external devices such as GPS receivers, barcode scanners, and Bluetooth modules communicate with PCs using UART. The devices send data packets to the PC, and the PC responds with commands and instructions.
**Industrial Automation:** In industrial automation applications, UART is used for communication between programmable logic controllers (PLCs) and other industrial equipment such as sensors, actuators, and motors. The PLCs send commands to the equipment, and the equipment responds with status updates and sensor readings.
Robotics: In robotics, UART is used for communication between the main controller and the motor controllers. The main controller sends commands to the motor controllers, and the motor controllers respond with status updates and sensor readings.
**Smart Home Applications:** UART can be used in smart home applications for communication between smart home devices such as smart thermostats, smart locks, and smart lights. The devices send commands and data to the hub, and the hub responds with status updates and commands.
Overall, the UART protocol is a versatile and widely used communication protocol that enables devices to exchange data in various applications.

**Advantages:**
**Simplicity:** The UART protocol is simple and easy to implement, making it a popular choice for many applications.
Versatility: The UART protocol is used in a wide range of electronic devices, including microcontrollers, sensors, and communication modules.
**Cost-effective:** The UART protocol does not require any additional hardware other than a UART module or chip, making it a cost-effective solution for many applications.
Asynchronous transmission: The UART protocol uses asynchronous transmission, which means that data is transmitted without the use of a clock signal. This makes it easier to interface with different devices that may have different clock speeds.
**Error detection:** The UART protocol has built-in error detection mechanisms, such as parity bits and checksums, which help to ensure the integrity of the transmitted data.
Low power consumption: The UART protocol is designed to consume very little power, making it ideal for battery-powered devices.

**Disadvantages :**
**Limited distance:** The maximum distance that data can be reliably transmitted using the UART protocol is limited, typically to a few meters. This can be a disadvantage for applications that require longer transmission distances.
Limited speed: The speed of data transmission using the UART protocol is limited, typically to a few megabits per second. For applications that require higher data rates, other protocols such as SPI or I2C may be more suitable.
Sensitive to noise: The UART protocol is sensitive to noise and other electrical interference, which can cause errors in the transmitted data. This can be a disadvantage in environments with high levels of electromagnetic interference.
**No flow control:** The UART protocol does not provide flow control mechanisms, which can lead to data loss or corruption if the receiving device cannot keep up with the data rate.
Limited functionality: The UART protocol is a simple protocol that is primarily used for transmitting and receiving data. It does not provide support for more complex functions such as address recognition, multi-master communication, or error correction.

**Conclusion:**
The UART (Universal Asynchronous Receiver/Transmitter) protocol is widely used in digital communication between devices. It is a simple and robust protocol that allows for asynchronous serial communication between devices.
In conclusion, the UART protocol is a fundamental communication protocol that enables devices to exchange data reliably and efficiently. Its simplicity, low hardware requirements, and wide compatibility make it a popular choice in many applications, such as embedded systems, industrial automation, and communication between microcontrollers and peripherals. However, its asynchronous nature requires careful timing considerations, and its limited error detection capabilities may require additional error checking mechanisms to ensure data integrity.