quartz/content/notes/sequential-circuits.md
2022-07-26 12:08:12 +12:00

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---
title: "sequential-circuits"
aliases:
tags:
- cosc204
---
[combinatorial-logic-circuits](notes/combinatorial-logic-circuit.md) always produce the same outputs given the same input. Sequential curcuits on the other hand, produce different outputs depending on past history and the inputs.
![combinatorial vs sequential](https://i.imgur.com/GbfAZ4c.png)
There are two main types of sequential circuit
- Sychronous
- this is when changes of state occur in time with a clock cycle
- changes of input occur between clock pulses
- state changes occur at the clock pulses
- Asynchronous
- state changes occur as the inputs occur
- event driven
# Main circuits
## SR latch
The set reset latch is the most basic and simple sequential circuit
![simple sr latch with NOR gate](https://i.imgur.com/ay6uk33.png)
The ouput is remembered and changed basic on previous output.
- When S (set) is pulsed Q is one and Q̄ is zero
- When R (reset) is pulsed Q is set to zero and Q̄ is set to one
## D Flip FLop
![D flip flop with NAND gates](https://i.imgur.com/XVnK2s6.png)
The D flip flop is basically an SR connected to a clock. Instead
[circuit simulation](https://tinyurl.com/2cafc57y)
## Simple video demonstration of some sequential circuits
<iframe width="560" height="315" src="https://www.youtube.com/embed/I0-izyq6q5s?start=84" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>