Timers and PWM

A timer counts clock ticks (after a prescaler). Modes: overflow interrupts, compare match (generate events at exact times) and input capture (timestamp an edge to measure frequency or pulse width).

Pulse-width modulation switches a pin rapidly; the duty cycle $D$ sets the average:

$V_{avg} = D \cdot V_{CC} \qquad f_{PWM} = \frac{f_{clk}}{\text{prescaler} \times (\text{TOP} + 1)}$

PWM controls LED brightness, motor speed and servo position (servos expect a 1–2 ms pulse every 20 ms).