UART 101: Getting to Know Serial Communication

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Table of Contents

  1. Introduction
  2. What is UART?
  3. How Does UART Work?
  4. Basic UART Frame Structure
  5. Advantages of UART
  6. Limitations of UART
  7. Common Applications of UART
  8. Final Thoughts

Introduction

In the world of electronics and microcontrollers, communication between devices is essential. One of the most common ways to achieve this is through UART—short for Universal Asynchronous Receiver/Transmitter. This blog explores the fundamentals of UART, how it works, and why it's used so widely in embedded systems.

What is UART?

UART is a hardware-based communication protocol designed for asynchronous serial communication between two digital devices. It enables data transmission between microcontrollers, sensors, modems, computers, and other peripherals.

The term "asynchronous" indicates that no common clock is shared between the sender and receiver. Instead, UART uses specific signals and timing to ensure data is transferred reliably from one device to another. It's commonly found in development boards, routers, IoT devices, and many embedded systems.

How Does UART Work?

UART communication relies on two key components: the transmitter (TX) and the receiver (RX). The process is simple but efficient, ensuring smooth data flow between devices.

UART diagram
    1. Data Transmission
    • The transmitter sends data as a sequence of bits, one at a time.
    • Each data packet is framed with the following elements:
      • A start bit to signal the beginning of transmission
      • Data bits (usually 7 or 8 bits)
      • An optional parity bit for basic error checking
      • One or more stop bits to mark the end of the frame
    2. Data Reception
    • The receiver listens for the start bit to sync up with the data stream.
    • It then reads the incoming data bits in order.
    • If a parity bit is used, it verifies data integrity.
    • The stop bit confirms the end of that data packet.

Basic UART Frame Structure

A UART frame is a well-defined structure that ensures accurate communication between devices. Here’s a breakdown of what a typical UART data frame looks like:

  • Start Bit
    Marks the beginning of data transmission. It’s usually a logic low ('0') signal, signaling the receiver to get ready for incoming data.
  • Data Bits
    These are the actual bits of information being sent—typically 5 to 8 bits long, depending on the configuration.
  • Parity Bit (Optional)
    Used for basic error detection. It can be configured as even or odd parity based on whether the total number of '1' bits should be even or odd.
  • Stop Bit(s)
    Signals the end of the data frame. Usually one or more bits set to logic high ('1') to give the receiver time to process the frame.
UART frame diagram

Advantages of UART

  • Simplicity: UART is straightforward to set up and use, making it an excellent choice for simple serial communication needs.
  • Low Cost: Since UART doesn't require a separate clock line, it cuts down on wiring and hardware complexity.
  • Asynchronous Communication: Because there's no need for a shared clock signal, UART offers flexibility—allowing communication between devices running at different clock speeds.

Limitations of UART

  • Speed Constraints: UART is generally slower than synchronous protocols like SPI or I2C, making it less ideal for high-speed data transmission.
  • Short-Range Communication: It performs best over short distances. Beyond that, signal degradation and noise can become problematic.
  • Limited Device Support: UART is typically designed for point-to-point communication. Connecting multiple devices requires additional components like multiplexers or bus systems.

Common Applications of UART

  • Microcontroller Communication: UART is a go-to protocol for tasks like debugging, logging, or programming microcontrollers.
  • Embedded Systems: It plays a crucial role in connecting embedded systems to peripherals—such as sensors, displays, or GPS modules.
  • Computer Interfaces: UART is commonly found in serial interfaces (like RS-232), used for connecting computers to external hardware like modems or legacy devices.

Final Thoughts

Whether you're just stepping into embedded systems or working on a full-fledged hardware project, understanding UART gives you a solid communication foundation. Its simplicity, reliability, and widespread support make it an essential tool in any hardware hacker’s or developer’s toolkit.

Stay tuned for the next part of this series, where we dive into identifying UART pins on real hardware using a multimeter and some investigative skills.