# Homework Help: Logic Gates: Multiple ALUs?

1. Nov 28, 2004

### sjaguar13

If I have an 8-bit ALU, how would I hook them up to do the layer thing (I don't know the name)? It's the thing that you start with 4 ALUs, then they go down to 2, then those go down to 1. Are all the inputs for each of the original 4 seperate, or do they share some inputs? How to two go down to one? The outputs of one are the As of the next and the outputs of the other are the Bs of the next? What about the Cout, Zero, and Set? Do they somehow go into the next?

2. Nov 29, 2004

### e(ho0n3

What exactly are you trying to do here? You want to feed the output of two ALUs to one ALU and feed that to the remaining ALU? What's the spec. for these ALUs?

3. Nov 29, 2004

### sjaguar13

4. Nov 29, 2004

### e(ho0n3

The connections between the ALUs will depend on the application you are using them for. What do you want to do with them?

5. Nov 29, 2004

### sjaguar13

I want it to act in parallel. Looking at the 7 8-bit ALUs, I want it to be able to take 4 sets of numbers and get them down to 2 sets. Then, take those 2 sets and get it down to one. If I had 3 and 4, 3 and 5, 2 and 2, 1 and 2, and I select add, I want the first ALU to add 3 and 4 to get 7. Put the 7 into the next ALU. 3 and 5 get added for 8 and it goes down to the next ALU with the 7 for 15. 15 goes to the last ALU. 2 and 2 is 4 and that goes to the ALU along with 3 from 1 and 2. 4 and 3 is 7 and that goes to the last ALU with the 15 for 22, which is the answer.

If the answer from one becomes the input of the next, what about the Cout, Not B, and basically the other pins do?

6. Nov 29, 2004

### e(ho0n3

I see. If you don't need the other inputs, don't use them (set them to ground or something). Simple as that. In real life however, your parallel setup would suffer from propagation delays and whatnot. You can get rid of that however by putting in some registers and have everything synchronized to a clock.