UART Protocol in Embedded Systems: Overview and Qt Integration

Reliable device-to-device communication is at the heart of every well-designed embedded system. Whether you’re building a sensor gateway, configuring industrial hardware, or debugging a safety-critical medical device, having a robust and predictable hardware communication protocol is essential.

UART remains one of the most widely used serial communication protocols in embedded systems — not because it’s the newest, but because it’s simple, efficient, and well-supported across virtually all hardware platforms. In fact, it’s considered one of the earliest serial protocols still in common use today.

In this article, we’ll explore:

 

• what UART is and how it works,
• the practical advantages (and limitations) of using UART in embedded designs,
• how to seamlessly integrate UART communication into your software using the Qt framework

Need support implementing UART-based protocols or developing embedded system software?
Let’s talk about how we can support your team.

 

What is UART?

UART (Universal Asynchronous Receiver/Transmitter) is one of the simplest and oldest serial communication protocols in the embedded systems – in full form often referred to as an asynchronous receiver transmitter UART. It enables two electronic devices to exchange serial data over just two wires: a transmit line (TX) and a receive line (RX) – commonly known as the UART data transmission line.

Unlike synchronous protocols (e.g. SPI or I²C), UART is asynchronous communication – there is no shared internal clock signal between the devices. Instead, each UART transmitter and receiver must agree on a data rate (transmission speed) and framing format in advance. Every data frame is wrapped with special bits (start and stop bits, and optionally an even parity bit matches rule) so the receiver can synchronize to the sender’s timing on the fly. The arrangement of these elements defines the overall data format and ensures each data packet is interpreted correctly. This start-stop framing allows UART devices to send data at arbitrary intervals without an external clock, hence “asynchronous.”

In practice, a UART link is typically point-to-point: it connects two devices directly, such as a microcontroller and a PC, or an MCU and a peripheral module, often referred to simply as a UART connection.

 

 

Where is UART used?

UARTs are ubiquitous in embedded systems. They often serve as the console or debug interface on development boards, allowing developers to log messages or transmit data commands. They are used to connect GPS receivers, Bluetooth/Wi-Fi modules, GSM modems, RFID readers, and countless other peripherals that stream data serially.

In many microcontrollers, a UART is a built-in peripheral, and the classic PC serial port is a UART implementing the RS-232 standard voltage levels. Modern PCs may lack physical RS-232 ports, but USB-to-UART converter cables are widely used to interface computers with embedded devices’ UART pins. Overall, UART remains popular because of its simplicity and low overhead for short-distance data communication (typically up to 15–20 meters over direct wires, or around 50 feet at most without special line drivers) – although with proper hardware support, it can also be adapted for certain long distance data transfers.

 

 

Advantages and Disadvantages of UART

Like any communication channel, UART has its pros and cons. It’s important for engineering teams and decision-makers to understand where UART excels and where its limitations might impact a project.

 

Advantages of UART:

• Simplicity and Low Cost: UART is straightforward and well-supported. Hardware implementation is easy and inexpensive – virtually all microcontrollers include one or more UART ports built-in. This simplicity makes UART communication easy to set up and debug, which can reduce development time.

 

• Minimal Wiring: Only two data lines are needed for full-duplex communication (plus ground) – the transmitting UART pulls the TX line high or low depending on each significant bit being sent.There is no separate clock line required, unlike I²C or SPI. Fewer wires mean simpler PCB layouts and connectors compared to parallel communication methods.

 

• No Addressing Overhead: UART is a direct one-to-one link between two endpoints, so no software addressing or complex bus arbitration is needed to identify who’s talking. This makes the protocol lightweight with very low overhead per packet, especially when working with a fixed data length.

 

• Basic Error Checking: An optional parity bit can be enabled to provide rudimentary error detection on each byte. While not robust against all errors, it can catch a single odd number of bit flips, offering a simple integrity check without extra software.

 

• Flexible Framing: The frame format (data bits, parity, stop bits) is configurable and can match different application needs such as parallel data conversion or specific clock cycle timing requirements. As long as both sides agree, you can, for instance, use 7-bit data with odd parity, or 9-bit frames for specialized use cases.

 

• Cross-Platform & Legacy Support: UART has been around for decades and is universally supported across platforms. From tiny 8-bit MCUs to PCs, nearly every system has a UART interface or can easily add one. This broad support means UART is great for interoperability and interfacing with old or legacy equipment that uses a data bus.

 

Disadvantages of UART:

• Point-to-Point Only: A UART link generally connects only two devices. There is no built-in support for addressing multiple devices or multi-drop networks. (Multi-device serial networks require external transceivers and protocols – for example, RS-485 hardware allows multi-drop wiring, but you must implement your own addressing scheme at a higher protocol layer.) For applications needing many nodes on one bus, UART alone isn’t the ideal choice.

 

• Requires Agreed Settings: Because it’s asynchronous, both sides must use the exact same baud rate and frame settings so that the transmitting UART receives data and the receiving side interprets each data packet correctly. If these parameters don’t match, communication will fail or produce garbled data. For successful communication, baud rates and framing must be consistent.

 

• Limited Data Rate and Distance: UART is relatively slow compared to modern communication interfaces. Practical baud rates top out around a few hundred kilobits per second in many embedded scenarios (115.2 kbps is a common default maximum). Higher speeds are possible but more susceptible to timing mismatches and line noise. Without specialized drivers, the cable length for reliable UART transmission is quite limited.

 

• No Robust Error Handling or Framing: Aside from the parity bit, UART has no built-in error correction or packet acknowledgement. If bytes are corrupted or dropped, the UART hardware won’t automatically request retransmission. Ensuring data integrity often requires checking the actual data against checksums at a higher layer.

 

• Half-Duplex Communication Patterns: Although the UART hardware interface itself is full-duplex (separate TX and RX pin lines can operate simultaneously), in practice many UART-based protocols use request-response exchanges that behave like half-duplex.

 

• Flow Control Needs Management: UART does not inherently prevent buffer overruns. A fast transmitting device could overflow a slow receiver’s buffer if the receiver cannot process data quickly enough. To mitigate this, flow control mechanisms can be used – either hardware flow control (additional RTS/CTS lines to signal when to pause/resume transmission) or software protocols (XON/XOFF characters). However, these are add-ons rather than a core part of UART, and implementing them adds complexity. Decision-makers should ensure that if large bursts of data are expected, some flow control or buffering strategy is in place to prevent data loss.

 

 

Qt and UART – Overview

As you may already know, the Qt framework provides robust libraries for implementing various communication protocols – and UART is no exception. Qt includes a module called Qt Serial Port (introduced as an official add-on in Qt 5) that makes it straightforward to integrate UART-based communication into your application. Instead of dealing with low-level OS-specific APIs (like Win32 CreateFile for COM ports or POSIX termios on Linux), you can use Qt’s high-level classes to open serial ports and exchange data in a platform-independent way.

Whether you need to interface with an embedded device over a physical RS-232/UART port or communicate with a USB virtual COM port, Qt has you covered with a unified API that supports efficient data transfer and simplifies handling of receiving serial data in event-driven applications. The same Qt code can run on a desktop PC, an embedded Linux board, or another supported platform, greatly simplifying development and improving portability.

 

 

Why Use Qt for UART Communication?

Apart from the general benefits of Qt (a rich C++ framework, powerful GUI tools), there are three key advantages to using Qt specifically for UART communication:

 

High-Level Abstraction

Qt provides an intuitive, high-level API for serial ports, so you can avoid the tedium of writing platform-dependent code or wrestling with low-level byte handling. In native code, handling a UART might involve different system calls or driver libraries on each OS. By contrast, Qt’s QSerialPort class abstracts all those details behind a clean interface. You can open a port and read/write data with just a few function calls. Configuration of port parameters (baud rate, parity, etc.) is done via simple setters on QSerialPort, rather than dealing with ioctl structs or Windows DCB configurations.

 

Cross-Platform Support

Using Qt for UART communication ensures your code is portable across operating systems and hardware platforms. Qt Serial Port is available on all major desktop OSes and many embedded platforms, using the appropriate backend for each. For example, the same QSerialPort code can run on an embedded Linux device or on Windows – Qt will use POSIX termios calls under the hood on Linux, and the WinAPI on Windows, but this is transparent to you as the developer. There’s no need to rewrite serial handling for each OS, or to include conditional compilation for different frameworks.

 

Efficient Event-Driven Model

Qt’s signal-slot mechanism is a perfect match for asynchronous serial communication. Rather than writing loops to poll the port or blocking a thread waiting for data, your application can react to UART events in an event-driven manner. For example, QSerialPort emits a readyRead() signal whenever new data arrives in its input buffer. You can connect this signal to a slot in your code that immediately reads and processes the incoming data. This means no manual polling and no wasted CPU cycles checking for data.

 

Qt Serial Port API Highlights

Qt’s Serial Port module offers a couple of key classes to implement UART communication easily in C++:

 

• QSerialPort – The central class representing a serial port device. You use QSerialPort to configure the port (baud rate, data bits, parity, stop bits, flow control) and to perform read/write operations.
• QSerialPortInfo – A helper class for discovering and describing serial ports on the system. QSerialPortInfo can enumerate all available ports and provide information like the port name, manufacturer, and serial number, which is useful for populating a list of ports for the user to select.

 

Practical Example – Communication protocol UART in Qt Application

To illustrate how Qt makes UART integration easy, let’s consider a simple example scenario.

 

Connecting to a Serial Device

Configure the serial port with the most common settings (115200 baud, 8 data bits, no parity, one stop bit, no flow control)

 

 auto serialPort = new QSerialPort(this);
#ifdef Q_OS_WIN
    serialPort->setPortName("COM1");
#else
    serialPort->setPortName("/dev/ttyUSB0");
#endif
    serialPort->setBaudRate(QSerialPort::Baud115200);
    serialPort->setDataBits(QSerialPort::Data8);
    serialPort->setParity(QSerialPort::NoParity);
    serialPort->setStopBits(QSerialPort::OneStop);
    serialPort->setFlowControl(QSerialPort::NoFlowControl);

    if (!serialPort->open(QIODevice::ReadWrite)) {
        qWarning() << "Error opening serial port:" << serialPort->errorString();
    }

 

Reading and Writing Data (Asynchronous I/O)

Asynchronous read handler: triggered whenever new data is available on the serial port

 

connect(m_serialPort, &QSerialPort::readyRead, this, [this]() {
        QByteArray chunk = m_serialPort->readAll();
        if (!chunk.isEmpty()) {
            m_buffer.append(chunk);
            processBuffer();
        }
    });

 

Error Handling and Closing

Basic error handling: log the error and close the port. In production code, you might also notify the user or attempt to reconnect after a delay.

 

connect(m_serialPort,
            &QSerialPort::errorOccurred,
            this,
            [this](QSerialPort::SerialPortError error) {
                qWarning() << "Serial port error:" << error;
                m_serialPort->close();
				 // Here one could emit error signal to the UI, schedule a retry, etc.
            });

 

Takeaways

For decision-makers, the takeaway is that Qt enables rapid development of robust serial communication features. Instead of writing and maintaining separate serial code for each platform (and dealing with the nuances of each), your team can leverage Qt’s unified API. This leads to less bugs and a faster time-to-market, as the heavy lifting of byte-level communication and cross-platform compatibility is handled by Qt’s libraries. Moreover, because Qt integrates the UART handling into its event loop, your application design stays clean and responsive — which is crucial for modern embedded interfaces that often combine real-time data display with user interactivity.

Need expert help implementing UART-based protocols or building high-performance embedded applications with Qt? Let’s talk about how we can support your team.