Clock

A clock is a periodic signal that alternates between logic 0 and logic 1 at a fixed rate. In synchronous digital circuits, it acts as the timing reference that coordinates when memory elements are allowed to update.

Key Parameters

• Clock cycle: (or period) time duration for each pulse, in seconds
• Clock frequency: number of cycles per second, in Hertz ($\text{Hz}$)
• Duty cycle: the fraction of one period the signal is HIGH

$\text{Clock Frequency}=1/\text{Clock Cycle}$

Clock Edges

The transition points of the clock are known as clock edges. A clock edge can either be rising (0 -> 1) or falling (1 -> 0). Most components act upon clock edges, see level & edge-triggering for the distinction in the two types of component behaviour.

Using a clock edge transition helps keep circuit behaviour predictable. Output change at one defined moment instead of continuously. The majority of all modern circuits designed will use a clock and edge-triggered components.

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