please dont rip this site

Digital Logic Tutorial

Binary Full Adder

If you can't see the simulation below, try the Full Adder Simulation on

Adding a pair of one digit binary numbers isn't that impressive, but digital logic builds, from the absurdly simple to the massively complex. The trick is to make the simple circuit into a block, or module, that you can use to build more complex circuits. The circuit on this page is set up to be that sort of "stackable" block. It has an Input box and an Output box which define the inputs and outputs of the block. And it has an extra input, Carry In or Ci, which can be used to accept the Carry Output from the prior digit. Basically, that means it can add THREE one digit binary numbers. Just like adding:


You add the 9 and the 1, which gives you the 0 and you have to "carry" the 1 over on top of the 3. Then you have to add THREE numbers: 1+3+2=6. In the same way, this more complex adder, allows you to add three binary digits, so you can add in the carry from the previous column. We will see that in the next circuit. For now, just look at how this circuit works. It's pretty complex, huh? It helps to look at the output, and figure out what combination of inputs should turn that output on.

This table shows the output we want for each possible input. It's call a truth table and it really does help when developing a circuit.

A B Ci S Co
0 0 0 0 0
0 0 1 1 0
0 1 0 1 0
0 1 1 0 1
1 0 0 1 0
1 0 1 0 1
1 1 0 0 1
1 1 1 1 1

You could actually just go down the table, and build a circuit by looking for any output that needs to be a 1, then describing a circuit that would only put out a 1 with that exact combination of inputs. For example, the second line of the table, the output for S could be described as: NOT A AND NOT B AND Ci. The next line would be NOT A AND B AND NOT C. Those can be combined into NOT A AND (NOT B AND Ci) OR (B AND NOT C). But really? You just fire up Logic Friday^ and put in the truth table and let it figure out the circuit for you.


Big Binary Adder

See also:

file: /Techref/logic/fulladder.htm, 5KB, , updated: 2017/9/16 21:43, local time: 2024/7/23 03:55,

 ©2024 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?
Please DO link to this page! Digg it! / MAKE!

<A HREF=""> Digital Logic Tutorial: Full Binary Addition Circuit</A>

After you find an appropriate page, you are invited to your to this massmind site! (posts will be visible only to you before review) Just type a nice message (short messages are blocked as spam) in the box and press the Post button. (HTML welcomed, but not the <A tag: Instead, use the link box to link to another page. A tutorial is available Members can login to post directly, become page editors, and be credited for their posts.

Link? Put it here: 
if you want a response, please enter your email address: 
Attn spammers: All posts are reviewed before being made visible to anyone other than the poster.
Did you find what you needed?

  PICList 2024 contributors:
o List host: MIT, Site host, Top posters @none found
- Page Editors: James Newton, David Cary, and YOU!
* Roman Black of Black Robotics donates from sales of Linistep stepper controller kits.
* Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters.
* Monthly Subscribers: Gregg Rew. on-going support is MOST appreciated!
* Contributors: Richard Seriani, Sr.

Welcome to!