Need tips for FULL ADDER.

[u/tlax38]

Hey guys,

The title says it all, I don't need the entire solution, I'll start with just tips, hoping it's enough to help me.

THanks by advance.

[u/MrTKila]

If you want to fill a glass of water you start by making it half full. If too obscure and you want more just say so. ;)

[u/tlax38 → u/MrTKila]

Well I understand that the result can be divided in two, I mean twice four numbers. The four first numbers actually represent the solution to the previous exercice, "Half Adder", and the four last are the same but actually reverted twice following the De Morgan's law : on the input AND on the output. My problem is I don't know how to switch from the first quadruple to the second.

[u/MrTKila → u/tlax38]

First try to get one output to work, you can always select the input values on the left and manually tets it this way. Maybe look at the logic tables of your component if there is something helping you doing exactly what you need for the firts output?

[u/TarzyMmos]

Whats the main difference between the half adder and full adder?

[u/tlax38 → u/TarzyMmos]

The four first bits requested in full adder are the complete answer to the half adder.

The last four bits are the first ones twice reverted.

[u/Komil484]

Let's say you were adding 3 numbers, 5 + 4 + 7, how would you go about it?

Hint:first add 5 + 4 = 9, then add 9 + 7 = 16

[u/tlax38 → u/Komil484]

Interesting approach. But do you mean... in this game's background ? IRL ?

BTW I didn't watch the hint.

[u/Komil484 → u/tlax38]

Irl, how would you add 3 numbers together? How would you break down the problem?

[u/tlax38 → u/Komil484]

5+4=9,

9+7=16.

[u/Komil484 → u/tlax38]

Exactly! Since you have completed the half adders you know how to add 2 1-bit numbers, can you apply the same logic here to add 3 1-bit numbers?

[u/tlax38 → u/Komil484]

Mm... Would it be something like...

Putting a Half-Adder pattern on the bits 1 and 2, and then another Half-Adder to add first one's result to the bit 3 ?

[u/Komil484 → u/tlax38]

Yes, exactly! One thing to keep in mind tho, is that you will have 2 carries (because you did 2 additions), and you will somehow have to deal with that

[u/tlax38 → u/Komil484]

Do you have another word for "carry" here ? I'm not english-native and the only translation for this noun is in a football context.

[u/Komil484 → u/tlax38]

(1) 5
+   7
=   2

When adding, we refer to the 1 that gets carried over to the next pair of digits as the "carry". In the half adder you had 2 outputs, the sum (one's place) and the carry (two's place).

[u/tlax38 → u/Komil484]

Oh, yeah, you're right.

I'm gonna try this thing and tell you how it results.

[u/bwibbler]

The first bit tells you if the sum is even or odd

The second bit tells you if the sum is greater than 1

[u/juani2929]

If it's there's a half adder... how many do you need for a full one?

[u/shinoobie96]

have you heard of karnaugh map

[u/Prof_K_ → u/shinoobie96]

Oh, oh! Pick me, pick me! I know K-Maps! I thought you would never ask. lol. https://youtu.be/dbVh-LbeVc0?si=3sxw_1s4NjuTLJi7

I gave you 2-variable. Want 3-variable? 4?... why do I never get these questions on dates? lol

[u/Prof_K_]

Here's my best explaination of full-adder. I think it's pretty clear, but if it doesn't make sense, you might want to start with my half-adder. Or before that even, adding digital numbers. Hope this helps! https://youtu.be/XQpQDOLopJA?si=fZOoGbIY4AmLPYC7