[Day 7] UART Basics – Serial Communication with Your Microcontroller

So far, we’ve been blinking LEDs and setting delays—but now it’s time for your microcontroller to talk.

Meet UART – the simplest and most popular method of serial communication in embedded systems.

💬 UART = Universal Asynchronous Receiver Transmitter

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🧠 What is UART?

UART is a hardware peripheral that allows two devices to exchange data one bit at a time, over just two wires:

• TX (Transmit)
• RX (Receive)
  

It’s asynchronous, which means:

• No external clock line is needed.
• Both devices must agree on a baud rate (bits per second).
  

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🔌 Common UART Applications

Use Case	Example
Debugging via Serial	Serial monitor (USB ↔ UART)
MCU-to-MCU Communication	Master-slave setups
GPS Modules	Send NMEA strings to MCU
Bluetooth Modules	HC-05, HC-06

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🔧 UART Communication Basics

Each character sent is framed like this:

Start Bit | Data Bits (usually 8) | Optional Parity | Stop Bit

Example: Sending character A (0x41)

Start | 0 0 0 0 0 0 1 0 | Stop

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📟 Simple UART Code Example (Bare-Metal)

Let’s assume these are the UART register addresses (for demo only):

#define UART_TX_REG      (*((volatile uint32_t*)0x4000C000))
#define UART_STATUS_REG  (*((volatile uint32_t*)0x4000C004))
#define UART_TX_READY    (1 << 0)

void uart_send(char c) {
    while (!(UART_STATUS_REG & UART_TX_READY)); // Wait until TX ready
    UART_TX_REG = c;                            // Send character
}

Send a string:

void uart_send_string(const char* str) {
    while (*str) {
        uart_send(*str++);
    }
}

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🧪 Real Use Case: Debugging

Want to see values in your embedded code without a screen? Just send it over UART:

char buffer[20];
sprintf(buffer, "Temp = %d\n", temp);
uart_send_string(buffer);

And view it in a Serial Terminal like:

• Arduino Serial Monitor
• PuTTY
• RealTerm
  

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📘 UART Settings You Must Know

Parameter	Typical Values
Baud Rate	9600, 115200
Data Bits	8
Parity	None, Even, Odd
Stop Bits	1
Flow Control	None (default)

💡 Both devices must match these exactly!

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🧰 Tools You’ll Need

• USB-to-Serial Converter (e.g., FTDI, CP2102)
• Serial Terminal Software
• Logic Analyzer (optional, for debugging)
  

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⚠️ Pro Tip

UART is full-duplex—TX and RX can run at the same time—but not every implementation supports this well. Also, use interrupts or DMA for better performance in real-time systems.

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🔍 Up Next (Day 8):

🧠 Interrupts – Stop Polling, Start Responding
Discover how microcontrollers respond instantly to events like button presses, sensor triggers, and more.