What is the STM32F4-Discovery Board?

The STM32F4-Discovery (official part number: STM32F407VGT6) is a low-cost evaluation board from STMicroelectronics designed to help developers learn and prototype with the ARM Cortex-M4 processor family. It costs around $15–20 USD and packs a tremendous amount of hardware for that price.

This board is widely used in universities, embedded systems courses, and professional prototyping because it gives you direct access to all major peripherals — GPIO, UART, SPI, I2C, CAN, USB, ADC, DAC, Timers, and DMA — without needing external components to get started.

STM32F407VGT6 MCU Specifications

The heart of the board is the STM32F407VGT6 — a 32-bit ARM Cortex-M4 processor with hardware floating-point unit (FPU). Let’s break down every specification:

Board Diagram Walkthrough

Here is a labeled diagram of the STM32F4-Discovery board showing the location and function of every major component:

ST-LINK V2 Debugger

The top portion of the Discovery board contains a complete ST-LINK V2 debugger built around a second STM32 MCU — the STM32F103C8T6. This means you only need a USB cable to program and debug your application — no separate JTAG programmer needed.

How ST-LINK Works

When you connect the board to your PC via the USB Mini-B connector (CN1), the STM32F103 enumerates as a USB HID device and exposes the SWD (Serial Wire Debug) interface to the target STM32F407. STM32CubeIDE (or OpenOCD) communicates with it to:

• Flash your compiled binary to Flash memory
• Set hardware breakpoints (up to 6 simultaneously)
• Inspect/modify registers and memory in real time
• Use ITM/SWO for printf() without UART (Virtual COM Port)

The CN3 header (5-pin SWD connector on the board edge) lets you use the on-board ST-LINK to program an external STM32 board. This makes the Discovery board useful as a standalone programmer.

On-Board User LEDs

The STM32F4-Discovery has four user-controllable LEDs — a perfect “Hello World” for any embedded systems course. Each LED is connected to a GPIOD pin through a 470Ω current-limiting resistor.

All four LEDs are connected between the MCU pin and VDD (3.3V) through resistors. The LEDs are active HIGH — setting the GPIO pin HIGH turns the LED ON. Here is the minimal bare-metal code to blink the green LED:

/* Bare-metal LED blink — no HAL, no libraries */
#include <stdint.h>

/* Base addresses from STM32F407 reference manual */
#define RCC_BASE   0x40023800
#define GPIOD_BASE  0x40020C00

/* Register offsets */
#define RCC_AHB1ENR (*((volatile uint32_t*)(RCC_BASE   + 0x30)))
#define GPIOD_MODER (*((volatile uint32_t*)(GPIOD_BASE + 0x00)))
#define GPIOD_ODR   (*((volatile uint32_t*)(GPIOD_BASE + 0x14)))

int main(void) {
    /* Step 1: Enable GPIOD clock (bit 3 of RCC_AHB1ENR) */
    RCC_AHB1ENR |= (1U << 3);

    /* Step 2: Set PD12 as output (MODER bits [25:24] = 01) */
    GPIOD_MODER &= ~(0x3U << 24);  /* clear bits */
    GPIOD_MODER |=  (0x1U << 24);  /* set output mode */

    while(1) {
        GPIOD_ODR |=  (1U << 12);   /* PD12 HIGH — LED ON  */
        for(volatile int i = 0; i < 500000; i++);

        GPIOD_ODR &= ~(1U << 12);  /* PD12 LOW  — LED OFF */
        for(volatile int i = 0; i < 500000; i++);
    }
}

User Push Button (B1)

There is one user-accessible push button on the board labeled B1 (sometimes marked as USER). It is connected to PA0 (Port A, Pin 0).

/* Read button state — PA0 is active HIGH */
#define GPIOA_BASE  0x40020000
#define RCC_AHB1ENR (*((volatile uint32_t*)0x40023830))
#define GPIOA_MODER (*((volatile uint32_t*)(GPIOA_BASE + 0x00)))
#define GPIOA_IDR   (*((volatile uint32_t*)(GPIOA_BASE + 0x10)))

void button_init(void) {
    RCC_AHB1ENR |= (1U << 0);    /* enable GPIOA clock */
    /* MODER bits [1:0] for PA0 = 00 (input mode, default) */
    GPIOA_MODER &= ~(0x3U << 0);
}

uint8_t button_read(void) {
    return (GPIOA_IDR >> 0) & 0x1;  /* returns 1 if pressed */
}

MEMS Accelerometer

The STM32F4-Discovery includes a MEMS 3-axis accelerometer. Original boards use the LIS302DL (discontinued); newer revisions use the LIS3DSH. Both communicate via SPI1.

The accelerometer measures ±2g / ±4g / ±8g. You can tilt the board and read X, Y, Z acceleration values. This is commonly used to demonstrate SPI communication (Tutorial 14) and interrupt-driven sensor reading (Tutorial 08).

Audio Codec (CS43L22)

The CS43L22 is a 24-bit, 96kHz stereo DAC from Cirrus Logic. It’s connected to the STM32F407 via two interfaces:

• I2C3 — for control/configuration (register writes to set volume, sample rate, etc.)
• I2S3 (I2S protocol over SPI3 pins) — for streaming audio data (PCM samples)

The 3.5mm stereo audio output jack (CN6) is driven by the CS43L22. The I2C address is 0x94 (write) / 0x95 (read).

USB OTG Connectors

The STM32F407 has two full USB OTG controllers. The Discovery board exposes both:

Power Supply System

Understanding the power system prevents frustrating “my board doesn’t work” scenarios. The Discovery board can be powered in multiple ways:

Power domains on the STM32F407:

• VDD (1.8–3.6V): Main digital power for CPU, Flash, peripherals
• VDDA (1.8–3.6V): Analog power for ADC, DAC, comparators, oscillators. Should be filtered separately.
• VBAT (1.65–3.6V): Battery backup domain — powers RTC, backup SRAM, LSE oscillator when main VDD is off
• VDD_USB: Regulated separately for USB transceiver (typically from a 3.3V LDO fed by 5V USB)

On-Board Crystals

The Discovery board has two crystal oscillators:

Extension Connectors (P1 and P2)

Two 50-pin expansion connectors (P1 and P2) break out all user-accessible STM32F407 pins. These are the connectors you use to wire up external sensors, displays, and modules on a breadboard.

Pin numbering on the connectors starts from pin 1 (marked with a dot on the PCB silkscreen). The pitch is 2.54mm (0.1 inch), compatible with standard jumper wires and breadboards.