🚗 STM32 DC Motor Control Using L293D — Register-Level Coding

This is a bare-metal STM32 DC motor control project using a register-level approach (no HAL drivers).
You’ll control a DC motor’s direction and speed using an L293D motor driver and manually configured STM32 registers.

This is great if you want to learn how microcontrollers really work under the hood — not just call HAL wrappers.

📌 What This Project Does

You’ll learn how to:

• Directly configure GPIO registers to set motor direction
• Set up PWM using STM32 timers at the register level
• Drive a DC motor via the L293D H-bridge driver
• Understand the signal flow from MCU → driver → motor

This is the same control strategy as HAL versions, just without abstraction layers.([DeepBlue][1])

🧠 Why Register-Level Code

Using registers means:

✔ You know what’s happening inside your MCU
✔ Code runs faster with minimal overhead
✔ You learn how to control peripherals manually
✔ Great for interviews and deep embedded skills

No HAL, no Cube — just straight C and register access.

📦 Hardware Required

Remember, DC motors should not be driven directly from MCU pins — that’s what L293D is for.([Last Minute Engineers][2])

🔌 Pin Connections (Example)

⚠️ Common ground between MCU, L293D, and motor supply is crucial.

🧩 How It Works — Beginner View

➤ Direction Control

Here we use GPIO register writes instead of HAL.

To rotate forward:

GPIOA->ODR |= (1 << 12);   // PA12 = 1
GPIOA->ODR &= ~(1 << 11);  // PA11 = 0

To reverse:

GPIOA->ODR &= ~(1 << 12);  // PA12 = 0
GPIOA->ODR |= (1 << 11);   // PA11 = 1

To stop:

GPIOA->ODR &= ~((1 << 12) | (1 << 11));

Direction bits map to L293D control pins, so changing them changes motor behavior.([Last Minute Engineers][2])

➤ PWM Speed Control (Register Style)

We manually configure the Timer (TIM) registers for PWM.

🔧 Basic Setup Steps

1. Enable Timer clock
2. Configure PWM pin as alternate function
3. Set timer period (ARR)
4. Set compare value (CCR)
5. Enable PWM mode

Example:

TIM1->PSC = 0;       // Prescaler
TIM1->ARR = 1000;    // Auto-reload (controls period)
TIM1->CCR1 = 500;    // Compare (50% duty)
TIM1->CCER |= TIM_CCER_CC1E; // Enable channel
TIM1->CR1 |= TIM_CR1_CEN;    // Start timer

This sets up PWM on Timer1 Channel1 with a duty cycle of 50%.
As you change CCR1, the speed changes.

Same concept as HAL PWM, just direct register access.([HackMD][3])

📌 Code Flow (Register Logic)

Here’s what your main loop actually does:

// Configure GPIO for direction pins
RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN;
GPIOA->MODER |= (1 << (12*2)) | (1 << (11*2)); // PA12, PA11 digital out

// Configure PWM pin
GPIOA->AFR[0] |= (1 << (5*4));   // Set AltFunc on PA5
// Timer setup for PWM here...

// Run motor forward
GPIOA->ODR |= (1<<12);
GPIOA->ODR &= ~(1<<11);

// PWM 50%
TIM1->CCR1 = 500;

// delay loop
for (volatile int i = 0; i < 1000000; i++);

// Stop motor
GPIOA->ODR &= ~((1<<12)|(1<<11));

This is pure bare metal, no layers between you and the silicon.

🔁 Internal Signal Flow

MCU Registers → GPIO Bits → L293D Inputs → Motor
MCU Timer → PWM Output → L293D EN → Motor Speed

Direction control is digital logic; speed control is PWM. Either one can be independently changed.

⚠️ Common Beginner Gotchas

❗ No HAL delays — use safe delay loops or SysTick
❗ Pin alternate function selection must match timer channel
❗ Always ensure proper grounding
❗ High duty cycles mean high motor current

🎓 What You’ll Learn

• How GPIO registers work
• Configuring timers for PWM
• H-bridge motor control logic
• How motor direction & speed signals affect movement

🚀 Next Steps You Can Build

• Button-controlled direction/speed
• UART motor control
• Encoder feedback + PID
• Integrating sensors

📜 License

MIT License — you’re free to use and expand.