# Why does my 8-bit adder say 1+3=6?

I have chained together the following full adder design given by the minecraft wiki eight times so that I can add together two 8-bit signals.:

For some odd reason the return of all the adders gives me `00000110` when I have inputted `00000011` and `00000001` respectively on the two input lines.

Is there something wrong with my design? Or am I just doing something really dumb?

• So you have some mechanism where you link eight of these. Have you considered the possibility that you're linking them wrong? We'd need the whole circuit to catch something like this. Also, you may want to link to the Wiki page that you're using. As is, I'm feeling too lazy to Google, but I might not be too lazy to click a link. Dec 22 '17 at 4:18
• I link the parts labeled C' and C together, yes. they are the carry flags for the adder. Supposedly if you chain these side by side next to each other they will form a circuit that adds two binary numbers. These inputs are represented by A and B. Dec 22 '17 at 4:25
• In binary, it's 001+011->110. So maybe the lower carry bit doesn't XOR, but just OR instead? But what's really causing it is impossible to know without knowing your circuit. Can you please upload a saved structure? Dec 22 '17 at 6:44
• @Fabian it's currently part of an Xbox One Windows 10 edition map so I'm not sure how I'd get a structure. Dec 22 '17 at 7:13
• You may want to try a few different inputs and see if they all have a similar offset as this particular example. That would help narrow down the problem. Dec 22 '17 at 9:19

Looking through the circuit, it looks like it should work

I went ingame and made one module of it, and cloned it 4x times, so it can add 4 bit numbers

``````  red    | 3 | 0011
+ blue   | 1 | 0001
= purple | 4 | 0100
``````

Looking into how to get results like yours, I found that you might be missing a redstone torch, or either of two redstone dusts

Removing one of the dusts causes the issue you're seeing

``````  red    | 3 | 0011