Telecommunication

What is UART Universal asynchronous receiver and transmitter

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UART: Universal Asynchronous Receiver and Transmitter Explained

A UART (Universal Asynchronous Receiver and Transmitter) is a ubiquitous peripheral device that facilitates serial communication between two devices. It's a fundamental building block for data exchange in various embedded systems, microcontrollers, and even personal computers for debugging purposes.

Key Characteristics of UART:

  • Serial Communication: UART handles data transmission one bit at a time over a single wire (typically) or two wires (for separate transmit and receive lines). This contrasts with parallel communication where multiple bits are transmitted simultaneously across multiple wires.
  • Asynchronous: UART communication is asynchronous, meaning there's no dedicated clock signal to synchronize the sender and receiver. Instead, the data stream includes additional control bits to indicate the start and end of a character, allowing the receiver to recover the clock signal from the data itself.

Components of a UART:

  • Transmitter (TX): Responsible for taking parallel data from a source (e.g., microprocessor) and converting it into a serial bit stream for transmission. It adds start and stop bits to frame the data and potentially parity bits for error checking.
  • Receiver (RX): Listens for the incoming serial bit stream, recovers the clock signal from the start and stop bits, removes the framing bits, and converts the serial data back into parallel data for the receiving device.
  • Control Logic: Manages the overall operation of the UART, including baud rate (data transmission speed) configuration, error handling, and buffer management for data flow control.

UART Communication Flow:

  1. Data Input: Parallel data is sent to the UART transmitter from the source device.
  2. Start Bit: The transmitter adds a start bit (typically a logic 0) to the data stream, signifying the beginning of a character.
  3. Data Bits: The actual data bits are transmitted sequentially, least significant bit first.
  4. Parity Bit (Optional): For error checking, a parity bit might be added based on the chosen parity scheme (even, odd, none).
  5. Stop Bits: One or two stop bits (logic 1) are added to indicate the end of the character and allow the receiver to resynchronize.
  6. Serial Transmission: The complete framed data (start, data, parity, stop) is transmitted serially over the communication line.
  7. Serial Reception: The receiver listens for the incoming serial bit stream.
  8. Start Bit Detection: The receiver detects the start bit and initiates the clock recovery process.
  9. Data Reception: The receiver captures the data bits and potentially the parity bit.
  10. Stop Bit Detection: The receiver confirms the end of the character by detecting the stop bits.
  11. Error Checking (Optional): Parity checking or other error detection mechanisms might be employed.
  12. Parallel Data Output: The received data, minus the framing bits, is converted back into parallel format and sent to the receiving device.

UART Applications:

UARTs are extensively used in various applications, including:

  • Microcontroller communication: Connecting microcontrollers to sensors, actuators, displays, and other peripherals.
  • Embedded system debugging: Connecting development tools to embedded systems for program loading, monitoring, and debugging.
  • Peripheral communication: Connecting devices like printers, modems, and barcode scanners to computers.
  • Industrial control systems: Facilitating communication between industrial controllers and various field devices.

UART Configuration:

  • Baud Rate: The data transmission speed in bits per second (bps). Common baud rates include 9600 bps, 115200 bps, and higher for faster communication.
  • Data Format: The number of data bits per character (typically 7 or 8) and the presence of parity bits (even, odd, none).
  • Stop Bits: The number of stop bits used (typically 1 or 2).

UART vs. Other Communication Protocols:

  • SPI (Serial Peripheral Interface): UART is simpler but slower than SPI. SPI is synchronous and often used for high-speed communication within a single device or short-distance connections between devices.
  • I2C (Inter-Integrated Circuit): Similar to UART in terms of data rate but uses a different communication protocol with a master-slave relationship. Often used for short-distance communication between integrated circuits on a PCB.

Conclusion:

UARTs are fundamental components for serial communication in numerous applications. Understanding their functionality, configuration options, and limitations is essential for anyone working with embedded systems, microcontrollers, or interfacing devices in various electronic projects. As technology advances, UARTs will likely continue to play a crucial role in facilitating reliable and efficient communication in various settings.

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