---
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>