Clocks and Reset

The heartbeat that paces every instruction.

A clock is a steady square wave that steps the CPU through instructions. A 16 MHz clock ticks sixteen million times a second, and simple instructions take one to a few ticks.

The clock source may be an internal RC oscillator (cheap, less accurate) or an external crystal (more accurate, needed for reliable serial timing). Higher clocks are faster but draw more current.

Reset forces the CPU back to a known starting state. Sources include power-on, a reset pin, a watchdog timer that fires when firmware hangs, and a brown-out detector that trips when the supply sags.