# Logic question, 3 input OR to 2 input OR

1. Sep 26, 2004

### mathrocks

Hi, I'm trying to convert a 3 input OR gate using only 2 input OR gates . How exactly will this look like?

Thanks

2. Sep 26, 2004

### enigma

Staff Emeritus
Convert it to what?

3. Sep 26, 2004

### mathrocks

to two 2 input OR Gates

4. Sep 26, 2004

### enigma

Staff Emeritus
I'm sorry. I'm still a little confused what your problem is asking.

Do you have the complete problem statement, or is this for independant work?

5. Sep 26, 2004

### mathrocks

Ok,

I need to build a 3 input OR gate using only 2 input NAND gates and inverters. The only way to do this is if I build the 3 input OR gate to use 2 input OR gates and then convert that into a NAND.

If you know how to build a 4 input OR gate using only 2 input OR gates that would be helpful also.

6. Sep 27, 2004

### Cliff_J

I think I answered this in another post. Cascade.

This is pretty simple. Draw out the truth table. You can get this result using one cent diodes...

Cliff

7. Sep 27, 2004

### Kenneth Mann

Simple, ground one input.

KM

8. Sep 27, 2004

### chroot

Staff Emeritus
I believe you read the problem statement incorrectly.

- Warren

9. Sep 27, 2004

### Kenneth Mann

You're probably right. The original statement isn't very clear. If the author wants to ust (multiple) dual input ORs to create a three input OR, the answer is just as simple. Feed the output of one OR to one input of a second OR. Then, the remaining three inputs comprise a Three Input OR.

KM

10. Sep 27, 2004

### Kenneth Mann

To get a four input OR simply feed two Two input ORs into a third Two input OR. Using three two input NANDs instead of ORs, do the same thing, but put inverters before each NAND input. This requires six (ugh) inverters. The problem using cascaded NANDs is that they automatically give you an AND (first stage)- OR (second stage) condition. What you want is an OR-OR condition. The simplest way to get this would be to feed two NORs into a NAND.

KM