What is a microcontroller?

A microcontroller (MCU) is a single integrated circuit that combines a CPU, memory (Flash + RAM) and a set of peripherals on the same die. Unlike a general-purpose CPU, an MCU is designed to run a single dedicated program forever, talking to the physical world through its pins.

Inside the chip

Every modern microcontroller is built from a few essential blocks:

• CPU core — typically ARM Cortex-M, RISC-V, AVR or Xtensa.
• Flash memory — non-volatile storage for your program (KB to MB).
• SRAM — fast volatile memory for variables and the stack.
• Peripherals — GPIO, timers, ADC, DAC, UART, SPI, I2C, USB, CAN.
• Clock + power — oscillators, PLLs, voltage regulators, sleep modes.
• Interrupt controller — lets hardware events preempt your code.

MCU families you should know

Peripherals — talking to the real world

Digital I/O (GPIO)

Each pin can be configured as input or output, HIGH or LOW. Used for LEDs, buttons, relays, and bit-banged protocols.

Analog (ADC / DAC)

The ADC samples a continuous voltage into a digital value (e.g. 0–4095 on a 12-bit ADC). Used for sensors, audio, and measurements.

Communication buses

• UART — simple async serial, perfect for debug logs and modems.
• I2C — 2-wire bus for sensors, EEPROMs and small displays.
• SPI — fast 4-wire bus for flash, displays and ADCs.
• CAN — robust automotive / industrial bus.
• USB / Ethernet / Wi-Fi / BLE — connectivity to the outside world.

Choosing the right microcontroller

Ask these questions before you commit to a part:

1. Power budget — battery life or always-on?
2. Performance — clock speed, FPU, DSP, AI accelerators?
3. Connectivity — Wi-Fi, BLE, Ethernet, LoRa, none?
4. Memory — does your firmware fit? Plus 30% headroom.
5. Toolchain — IDE, debugger, HAL quality, community.
6. Availability + lifecycle — can you buy 10k of them in 5 years?

Your first bare-metal program

Here is the canonical "blink an LED on PA5 of an STM32" — written in plain register-level C:

#include <stdint.h>

#define RCC_AHB1ENR  (*(volatile uint32_t *)0x40023830U)
#define GPIOA_MODER  (*(volatile uint32_t *)0x40020000U)
#define GPIOA_ODR    (*(volatile uint32_t *)0x40020014U)

int main(void) {
    RCC_AHB1ENR |= (1U << 0);          // enable GPIOA clock
    GPIOA_MODER &= ~(3U << (5 * 2));   // clear mode bits for PA5
    GPIOA_MODER |=  (1U << (5 * 2));   // set PA5 as output

    while (1) {
        GPIOA_ODR ^= (1U << 5);        // toggle PA5
        for (volatile int i = 0; i < 400000; i++) { } // crude delay
    }
}

Where to go next

Now that you understand the chip, learn the language and the operating system that drive it:

• Embedded C — pointers, registers, drivers and bit manipulation.
• Embedded RTOS — multi-tasking firmware with FreeRTOS.
• Arduino Basics — the gentlest starting point.
• IoT Weather Station — put it all together.