---
categories:
  - Computer Architecture
  - Electronics
  - Hardware
tags: [binary, memory, clock, electromagnetism]
---

# Clock signals

In the examples of digital circuits so far (i.e [adders](/Electronics_and_Hardware/Digital_circuits/Half_adder_and_full_adder.md) and [latches](/Electronics_and_Hardware/Digital_circuits/Latches.md)) everything happens in a single instant or over several repeated instances. This is because of how simple the circuits are. In the case of latches only a single bit is updated. And even with rippled adders they are just a series of 1-bit updaters in a chain.

With more complex circuits that use multiple memory devices which store a series of bits at once, we need a way to ensure that the bits are set at theB
A single iteration of the volatage rising and falling is a **pulse**. A complete oscillation from low to high and back to low is a **cycle**. As with all [electromagnetic](/Electronics_and_Hardware/Physics_of_electricity/Electromagnetism.md) signals we measure the frequency of the wave in Hertz: cylcles per second. We also further distinguish the rising and falling edge of a pulse. Rising represents the signal passing from ground to its maximum voltage and falling is the reverse (the electrons moving from the voltage source to ground).

The diagram below shows a pulse cycle of 2Hz.

![](/_img/clock_pulses.png)

## Linking components to the clock

- All components that need to be synchronised are connected to the clock
- State changes in the component occur only when a clock pulse occurs
- | Clock-driven components will typically trigger their state changes on either the rising edge or the falling edge of the pulse. |
- Components that trigger state changes on the rising pulse are **positive edge-triggered**
- Components that trigger state changes on the falling pulse are **negative edge-triggered**

The role of the clock is essential in the functioning of the [CPU](/Computer_Architecture/CPU/CPU_architecture.md#the-system-clock). It is the system clock that gives CPUs their performance rating: how many processes can execute within a given clock cycle.
