Timer Systems in Modern MCUs

Modern microcontrollers (MCUs) include versatile timer/counter modules that provide precise timing, waveform generation, and event capture functionality. Timers are used for:

• Generating delays and scheduling tasks
• Producing PWM signals for motor drives and LED dimming
• Measuring frequency, period, and pulse width of input signals
• Quadrature decoding for rotary encoders
• Event triggering and inter-peripheral synchronization

Prescaler

A prescaler divides the MCU clock frequency before it reaches the timer, allowing the timer to count at a slower, configurable rate. For example, a 72 MHz MCU clock with a prescaler of 72 will make the timer increment at 1 MHz. Prescalers are critical for:

• Adjusting timing resolution
• Extending maximum count period for long delays
• Generating specific output frequencies

Basic Timer / One-Shot Mode

Basic timers increment or decrement a counter based on the prescaled clock. - One-Shot Mode: Timer counts to a specified value and stops, generating a single event or interrupt. - Auto-Reload Mode: Timer resets automatically for periodic events.

Pulse Width Modulation (PWM)

PWM allows generation of a digital waveform with configurable duty cycle:

• Used for motor speed control, LED dimming, and audio signals
• Timer compares its counter to a capture/compare register
• When counter < compare value → output HIGH; else → output LOW
• Frequency determined by timer period, resolution by counter bits

Differential PWM / Dead-Time Control

For motor drives and H-bridge circuits, timers can output complementary PWM signals:

• Two outputs are 180° out-of-phase
• Dead time inserted to prevent both high- and low-side switches from conducting simultaneously
• Essential for safe operation in brushless DC and stepper motors

Input Capture

Input Capture allows a timer to record the counter value when an external event occurs:

• Measures pulse width, frequency, or period of external signals
• Can trigger interrupts on rising, falling, or both edges
• Used in sensors, encoders, and event timing applications

Quadrature / Encoder Timer

Timers can interface with quadrature encoders to measure rotation:

• Two-phase signals (A & B) indicate direction and position
• Timer counts increments/decrements based on signal edges
• Used in robotics, motor position sensing, and CNC systems

Advanced Timer Features

Modern MCU timers also support:

• Trigger outputs to synchronize other peripherals (ADC, DAC, PWM)
• External clock sources for specialized timing
• Master/Slave timer chaining for extended period
• Dead-time insertion for complementary outputs
• Gate control to enable/disable counting based on signals
• Event capture and compare match outputs for complex waveforms