STM32 Basics Interview Questions for Freshers
1. What is an STM32 microcontroller?
STM32 is a family of 32-bit ARM Cortex-M based microcontrollers developed by STMicroelectronics.
They are widely used in embedded and real-time systems due to their performance, low power consumption,
and rich peripheral set.
Interview Tip: Mention a real application like motor control, IoT devices, or industrial controllers.
2. Why is STM32 widely used in embedded systems?
STM32 is popular because of:
- ARM Cortex-M performance
- Low power modes
- Rich peripherals (Timers, ADC, DMA, USB, CAN)
- Strong ecosystem (CubeMX, HAL, LL)
- Long-term product availability
3. Which ARM Cortex cores are used in STM32?
STM32 microcontrollers use:
- Cortex-M0 / M0+
- Cortex-M3
- Cortex-M4 (with FPU)
- Cortex-M7 (high performance)
- Cortex-M33 (TrustZone support)
4. Arduino vs STM32 – What is the difference?
Arduino is designed for learning and rapid prototyping, while STM32 is used in production-grade
embedded firmware requiring real-time performance, low power, and hardware-level control.
5. What is CMSIS in STM32?
CMSIS (Cortex Microcontroller Software Interface Standard) is an ARM-defined abstraction layer
that provides:
- Standard register access
- Core peripheral definitions
- Compiler-independent APIs
STM32 Memory Architecture Interview Questions
6. Explain STM32 memory architecture.
STM32 memory includes:
- Flash (program storage)
- SRAM (stack, heap, variables)
- System memory (bootloader)
- Peripheral registers
- Option bytes
7. Flash vs SRAM in STM32?
Flash: Non-volatile, stores firmware
SRAM: Volatile, stores runtime data, stack, and heap
8. What is the vector table in STM32?
The vector table contains addresses of interrupt and exception handlers and
is located at the start of Flash or SRAM.
9. What is the stack pointer in ARM Cortex-M?
It points to the top of the stack and is automatically used during:
- Function calls
- Interrupt handling
- Context switching (RTOS)
10. What causes stack overflow in STM32?
Common causes:
- Large local variables
- Deep recursion
- Insufficient RTOS task stack size
Real Project Issue: Stack overflow often causes HardFault.
STM32 Clock and RCC Interview Questions
11. What is RCC in STM32?
RCC (Reset and Clock Control) manages:
- System clock source
- Peripheral clocks
- Reset control
12. HSI vs HSE in STM32?
HSI: Internal RC oscillator (less accurate)
HSE: External crystal (high accuracy, used in USB, CAN)
13. What is PLL in STM32?
PLL (Phase-Locked Loop) multiplies the clock frequency to achieve higher system speeds.
14. Why is clock configuration important?
Incorrect clock configuration leads to:
- Wrong baud rates
- Timer mismatch
- USB and communication failures
Interview Tip: Clock tree understanding is a common rejection point.
15. STM32 low power modes?
Used to reduce power consumption in battery-powered devices.
STM32 GPIO and Interrupt Interview Questions
16. GPIO modes in STM32?
- Input
- Output
- Alternate Function
- Analog
17. Push-pull vs Open-drain?
Push-pull: Drives both high and low
Open-drain: Requires external pull-up resistor
18. What is EXTI in STM32?
EXTI allows GPIO pins to generate external interrupts or events.
19. What is NVIC?
NVIC (Nested Vectored Interrupt Controller) manages:
- Interrupt priorities
- Interrupt nesting
20. Polling vs Interrupt?
Interrupts are more efficient and power-saving than polling.
STM32 Timer Interview Questions (High-Click Topic)
21. Types of timers in STM32?
- Basic timers
- General-purpose timers
- Advanced timers (motor control)
- Low-power timers
22. What is PWM in STM32?
PWM (Pulse Width Modulation) is used for:
- Motor speed control
- LED brightness
- Power regulation
HAL_TIM_PWM_Start(&htim3, TIM_CHANNEL_1);
23. What is input capture?
Used to measure:
- Signal frequency
- Pulse width
24. What is output compare?
Used to generate precise timing events without CPU intervention.
25. Timer frequency formula in STM32?
Timer Frequency = Timer Clock / (PSC + 1) / (ARR + 1)
STM32 Communication Protocol Interview Questions
26. UART vs USART?
USART supports both synchronous and asynchronous communication.
27. How does SPI work?
SPI is a full-duplex master-slave protocol with high data rates.
28. How does I2C work?
I2C uses:
- SDA (data)
- SCL (clock)
- Address-based communication
29. What is baud rate?
The speed of serial data transmission (bits per second).
30. What is DMA?
DMA transfers data between peripherals and memory without CPU involvement, improving performance.
STM32 ADC and Watchdog Interview Questions
31. ADC resolution in STM32?
Typically 12-bit, some series support higher resolution.
32. What is ADC sampling time?
The time taken by ADC to sample the analog input before conversion.
33. Continuous vs single ADC mode?
Continuous: Repeats automatically
Single: Converts once per trigger
34. What is watchdog timer?
Resets the MCU if firmware hangs due to software faults.
35. IWDG vs WWDG?
IWDG: Independent clock (more reliable)
WWDG: System clock based
STM32 HAL, Debugging, and Startup Interview Questions
36. What is STM32CubeMX?
A configuration tool for:
- Pin mapping
- Clock setup
- Peripheral initialization
37. HAL vs LL drivers?
HAL: Easy, portable
LL: Faster, closer to hardware
38. What is startup code?
Initial code that:
- Sets stack pointer
- Initializes memory
- Calls main()
39. SWD vs JTAG?
SWD uses fewer pins and is widely used for debugging.
40. What is HardFault?
Occurs due to:
- Invalid memory access
- Stack overflow
- Corrupted pointers
STM32 RTOS and Real-World Questions
41. What is FreeRTOS?
A real-time operating system used for multitasking.
42. What is context switching?
Saving and restoring task state when switching tasks.
43. Semaphore vs Mutex?
Semaphore: Signaling
Mutex: Mutual exclusion
44. What is priority inversion?
Low-priority task blocks a high-priority task.
45. How to reduce power consumption?
- Low-power modes
- Clock gating
- Efficient firmware design
46. How do you debug STM32 firmware?
Using:
- Breakpoints
- Registers
- Fault handlers
- SWD/JTAG debuggers
47. How do you interface sensors?
Using ADC, I2C, SPI, or UART.
48. How do you update STM32 firmware?
Via:
49. Most common STM32 interview mistake?
Ignoring clock configuration and interrupt priority.
50. Why is STM32 preferred for embedded jobs?
- Strong ecosystem
- ARM Cortex-M performance
- Industry-wide adoption
Conclusion
STM32 remains one of the most in-demand platforms in embedded systems and firmware engineering.
Mastering these 50 STM32 interview questions demonstrates not just theoretical knowledge,
but real-world firmware readiness.
Interviewers prefer candidates who can explain:
- Why a feature is used
- How it behaves in real projects
- What problems it solves
This guide is structured exactly with that mindset.
