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Understanding UART Communication

Posted:10:10 AM November 22, 2023 writer: iotbyhvm


The Universal Asynchronous Receiver Transmitter, or UART for short, is a crucial component in how our devices communicate with each other. It facilitates smooth information sharing, much like how people use language to communicate. The article discusses the benefits and drawbacks of UART, compares RS232 vs UART, shedding light on why it remains a popular choice for various applications. Readers can explore related materials, including details about the UART protocol, UART vs RS232 comparisons, and insights into UART speeds and baud rates, both through internal and external connections.

What is a UART - UART stands for Universal Asynchronous Receiver-Transmitter. It is a hardware device that facilitates serial communication between different devices. UART sends and receives data bits one by one, framed by start and stop bits, and uses external signaling levels to communicate with other devices. UART can be configured with different parameters, such as baud rate, data bits, parity bit, stop bits, and flow control. UART can also support IrDA protocols for infrared communication. UART can also communicate with devices that use different voltage levels, by using a level switch circuit. UART can be integrated in microcontroller chips, or used as a separate IC. UART can also be used for automobiles, smart cards, and SIMs.

How Uart Connects

A UART channel has two data lines. There is an RX pin and a TX pin on each device (RX for receive and TX for transmit). Each device’s RX pin is connected to the other device’s TX pin. Note that there are no shared clock lines! This is the “async” aspect of the universal async receiver sender. In simpler terms, UART is a hardware device that enables communication between different devices using only two wires. One wire is used for transmitting data, and the other wire is used for receiving data. Both ends of the communication also have a ground connection. UART communication offers three modes: simplex, where data travels in one direction only; half-duplex, where each side can speak but not simultaneously; and full-duplex, allowing both sides to transmit data simultaneously.

How UART Works

A UART connection is established using two dedicated data lines: RX (Receive) and TX (Transmit). Each device participating in the communication is equipped with both RX and TX pins. Significantly, the RX pin of one device connects to the TX pin of the other device, enabling the exchange of data through a UART connector. It's important to note that UART operates asynchronously, meaning there is no shared clock signal governing the communication, distinguishing it from synchronous protocols such as UART RS232.

How UART Works


  • Data Source:

The UART set to transmit receives data from a data bus.

  • Data Bus Usage:

The data bus acts as a conduit for sending data to the UART from another device, such as a CPU, memory, or microcontroller.

  • Parallel Transfer:

Data is transferred from the data bus to the transmitting UART in parallel form.

  • Data Augmentation:

The transmitting UART adds a start bit, a parity bit, and a stop bit to the parallel data, forming a complete data packet.

  • Serial Output:

The data packet is then output serially, bit by bit, at the Tx (transmit) pin.

  • Reception:

On the receiving end, the UART reads the serially transmitted data packet bit by bit at its Rx (receive) pin.

  • Parallel Conversion:

The receiving UART converts the received serial uart data back into parallel form.

  • Data Packet Reconstruction:

The start bit, parity bit, and stop bits are removed, reconstructing the original data packet.

  • Parallel Transfer (Receiving End):

Finally, the receiving UART transfers the reconstructed data packet in parallel to the data bus on the receiving end.

Fundamentally, UART is asynchronous, which means that it doesn't depend on the sender and recipient sharing a clock signal. Instead, it facilitates data transmission by using a predetermined set of settings. Devices can communicate fluidly because data can accurately communicate and receive when both the transmitter and the receiver share the same set of characteristics. Due to its ease of use and adaptability, UART is a popular option for everything from GPS modules to Bluetooth modules. UART Packet

UART transmits data in packets, and each packet is structured with 1 start bit, 5 to 9 data bits (depending on the specific UART configuration), an optional parity bit, and either 1 or 2 stop bits.

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Start bit

The start bit is the first bit in a UART data frame and serves as the initial signal to alert the receiver of the impending arrival of data. The start bit's exact duration depends on the selected baud rate, however it is normally a logical low (0) voltage level. The UART transmitter sets the voltage to this low level to initiate the data frame when it senses the need to send data. The receiver detects the dropping voltage as the start bit since it is continuously scanning the communication channel.

Once the receiver detects the start bit, it synchronizes its internal clock with the sender's, aligning itself with the expected arrival of the data bits. This synchronization ensures that it samples the subsequent data bits at precisely the right moments to accurately decode the transmitted information.

Data Frame

Data bits represent the actual information transferred from the sender to the recipient, often in binary form. You can change the number of data bits; eight bits are the most popular option, but it can be as few as five or as many as nine depending on the particular UART settings, uart pin out. Whether it's a character, number, or some other kind of data, these pieces express the main idea of the message.

The sender places the data bits in the data frame, and the receiver samples the data bits at preset intervals based on the agreed baudrate in uart after synchronizing with the start bit. The receiver then processes the data conveyed by the data bits, enabling the reconstruction of the transmitted data.


The "parity bit" is an additional bit added to the data frame for parity. It derives from the data bits and is positioned just before the UART stop bit or bits. Even and odd parity are the two types that are most prevalent. With "even" parity, the parity bit is set to ensure an even total count of "1" bits, while "odd" parity changes the parity bit for an odd total count of 1 bits.

The purpose of the parity bit is to detect errors in the received data. If the sender and receiver agree on using, for example, even parity, and the received data frame contains an odd number of "1" bits, the receiver immediately knows that an error has occurred. Similarly, with odd parity, an even number of "1" bits would indicate an error.

Stop bits

Stop bits are necessary to keep the sender and recipient in sync, which guarantees correct and dependable data processing. The receiver is informed that the current data frame has ended when uarts one login or more stop bits appear after the data bits. After processing the data bits and synchronizing with the start bit, the receiver knows to anticipate one or more uart stop bits. Without running the danger of data overflow or misinterpretation, this delay enables the receiver's internal circuits to reset and get ready for the receipt of the following data frame.

The choice between one or two stop bits depends on the specific requirements of the communication system. In most cases, one stop bit suffices, but two stop bits offer enhanced reliability and find use in data-critical environments.

Steps Of UART Transmission

UART (Universal Asynchronous Receiver Transmitter) transmission involves a series of steps that enable the asynchronous exchange of data between devices. Understanding these steps is crucial for anyone working with UART communication, uarts move in day 2023. Below are the key phases of UART transmission:

  1. The transmitting UART obtains data in parallel from the data bus.


2. The transmitting UART includes the start bit, parity bit, and stop bit(s) in the data frame.

3. The transmitting UART sequentially sends the entire packet to the receiving UART.

4. The receiving UART removes the start bit, parity bit, and stop bit from the data frame.

5. The receiving UART transforms the serial data back into parallel form and then transfers it to the data bus on the receiving end.

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People widely use UART (Universal Asynchronous Receiver Transmitter) communication due to its numerous advantages in various applications. Below are key advantages of UART communication:

1. Simplicity: UART is remarkably straightforward. It doesn't rely on complex handshaking or clock signals, making it easy to implement and troubleshoot. This simplicity is particularly advantageous for embedded systems and microcontroller-based applications.

2. Versatility: UART is highly versatile and can be used for point-to-point communication, multipoint communication, and even for daisy-chaining devices. Its wide applicability spans across industries, including industrial automation, telecommunications, and consumer electronics.

3. Robustness: UART chip can withstand challenging electrical environments and noise. It suits scenarios where data integrity is crucial, providing reliable communication even in less-than-ideal conditions.

4. Low Overhead: Compared to other communication protocols, UART serial has minimal overhead. It doesn't require the additional bits and framing that other protocols, such as Ethernet, demand. This efficiency is especially advantageous for low-bandwidth or resource-constrained applications.

5. Real-Time Communication: UART supports real-time rk communication, making it suitable for applications where immediate data transfer is required, such as robotics and industrial control systems.

6. Interoperability: UART is universally understood and supported by most microcontrollers, making it easy to UART vs USB, UART vs USART, UART interface with a wide range of hardware devices.

7. Low Cost: UART hardware implementations are cost-effective and readily available, contributing to its enduring popularity in both consumer and industrial products.

8. Minimal Latency: UART communication has minimal latency, which is important for applications where low delay is critical, such as robotics, GPS modules, and remote control systems.


While UART (Universal Asynchronous Receiver Transmitter) communication offers many advantages, it's not without its limitations. Understanding these disadvantages is important when choosing the right UART communication protocol for a specific application:

1. Half-Duplex: UART is typically half-duplex, UART meaning data can be transmitted in only one direction at a time. Is UART full duplex ? - Full-duplex communication (simultaneous two-way data exchange) often requires additional hardware and signaling, which can be a disadvantage in certain applications.

2. Speed Limitations: UART's baud rate, which determines the data transmission speed, is limited compared to other modern UART communication protocols. Less suitable for high-speed networking

3. Lack of Built-In Error Handling: UART lacks error-checking. While it can include a parity bit for basic error checking, it doesn't offer the robust error-handling capabilities found in protocols like Ethernet. This makes UART timing diagram less suitable for applications with stringent data integrity requirements.

4. Not Suitable for Large Networks: UART is typically used for point-to-point or simple multipoint communication. The system lacks UART address and routing features found in network protocols like TCP/IP and isn't designed for large-scale network applications

5. Cable Length Limitations: The effective cable length for UART communication is limited due to UART signals degradation over longer distances. UART 5 letter word. Communication over extended UART cable runs may require repeaters or signal boosters.

6. Lack of Flow Control: UART communication often lacks advanced flow control mechanisms, which can lead to data loss in scenarios where the sender is transmitting data faster than the receiver can process it.

7. Synchronization Challenges: Asynchronous communication, a fundamental feature of u a r t, can lead to synchronization issues when devices are running at slightly different clock speeds, potentially causing data loss or misinterpretation..


In conclusion, UART communication, with its simplicity, versatility, and long-standing reliability, remains a foundational protocol in the world of data exchange.  While it has its limitations, such as speed constraints and the lack of advanced error handling, its enduring popularity is a testament to its enduring relevance.

What are serial communication protocols or what is serial communication - Serial communication protocols transmit data sequentially, serial protocols transmits - bit by bit, often used in RS-232, SPI, I2C, and UART for inter-device communication.  How does serial communication work - Serial communication transmits data sequentially as a stream of bits, 1 bits, one after the other, using a single wire or channel.

UART is an excellent choice for many applications, particularly those emphasizing ease of implementation and robust, real-time communication. Its universal acceptance and cost-effectiveness make it a valuable tool for engineers, developers, and enthusiasts across a wide range of fields. Understanding the principles, what does uart stand for, its definition, UART pins or UART pinout, advantages, and disadvantages, as well as USART vs UART, equips us to make informed choices in utilizing this essential communication protocol for diverse electronic projects.


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