How do timers work in MCUs?
Timers in microcontrollers (MCUs) are hardware peripherals that count clock pulses to measure time intervals or generate precise time-based events. They’re fundamental for tasks like delays, PWM generation, event counting, and real-time control.
How Timers Work
A timer counts up (or down) based on a clock source. When the counter reaches a specific value (overflow or match), it can trigger an interrupt or an output event.
🔧 Core Components of a Timer
Counter Register
Stores the current count value.
Can be 8-bit, 16-bit, or 32-bit depending on the MCU.
Prescaler
Divides the input clock to slow down counting (e.g., divide 16 MHz by 16 = 1 MHz).
Allows adjusting the time base.
Auto-Reload or Compare Register
- Sets the value at which the timer resets or triggers an interrupt.
Interrupt Logic
- Fires an interrupt when the counter overflows or matches a value.
Control Registers
- Configure mode (up/down count, one-shot, continuous), enable/disable, etc.
Common Timer Modes
| Mode | Description |
| Basic Timer | Simple counting, delay generation |
| Periodic Timer | Repeats at fixed intervals (e.g., 1ms tick for RTOS) |
| PWM Mode | Generates Pulse Width Modulated signals |
| Input Capture | Captures timer value on an external event (e.g., signal edge) |
| Output Compare | Triggers an action when timer reaches a set value |
| Encoder Interface | Reads position data from rotary encoders (used in motor control) |
Example: Delay Generation
Assume:
MCU clock = 16 MHz
Prescaler = 16000 → Timer ticks at 1 kHz (1 ms per tick)
Auto-reload = 1000 → Timer overflows every 1000 ms (1 second)
So the timer interrupt occurs once per second.
Use Cases
Delays & timeouts
PWM for motor control, LEDs
Capturing signal duration (ultrasonic sensors)
Scheduling tasks in RTOS
Frequency and pulse measurement
