Solved

4-bit ALU

Posted on 2004-08-28
9
501 Views
Last Modified: 2007-12-19
hi
     i have searching the net for a good 4-bit alu design.i wanted a little help in this regard.
                              thanks
0
Comment
Question by:mack123
  • 3
  • 2
  • 2
  • +2
9 Comments
 
LVL 18

Expert Comment

by:JR2003
ID: 11923582
What are you looking for?
Is a circuit that will take four 4-bit numbers a, b, c and d and will evaluate: a+ b + (c * d) what you are looking for?
0
 
LVL 27

Expert Comment

by:aburr
ID: 11924143
you could use half the capabilities of a Z80 chip.
also look at the Basic Stamp series of chips
0
 
LVL 84

Expert Comment

by:ozo
ID: 11924173
Could you use a 74LS181 or 74F382 ?
0
 

Author Comment

by:mack123
ID: 11924199
any ic's could be used except the ALU ic.it has to be implemented.
so 74LS181 certainly cannot be used
0
Threat Intelligence Starter Resources

Integrating threat intelligence can be challenging, and not all companies are ready. These resources can help you build awareness and prepare for defense.

 

Author Comment

by:mack123
ID: 11924206
please if u find it on a website ,please do tell me.
0
 
LVL 84

Accepted Solution

by:
ozo earned 350 total points
ID: 11924210
0
 
LVL 18

Expert Comment

by:JR2003
ID: 11924913
This has the logical gate layout of 74LS181 which you could implement useing ICs with just ANDs, ORs and NOTs
http://www.visc.vt.edu/~mhsiao/ece4504/project/proj0/181_datasheet.pdf

Another simple solution is to use a programmable EPROM as a lookup taable. If you get one with 16 inputs and 16 outputs you can have a circuit that will do an operation on 4 4-bit numbers and produce a 16 bit result. The maximum result of the operation A + B + (C * D) where A, B, C and D are  4-bit numbers is exactly (2^16)-1 - the maximum 16-bit number which would fit in nicely with your requirement.
0
 
LVL 18

Expert Comment

by:JR2003
ID: 11924998
oops, I meant to say that you could get an EPROM with 16 inputs and 8 outputs!


Another simple solution is to use a programmable EPROM as a lookup taable. If you get one with 16 inputs and 8 outputs you can have a circuit that will do an operation on 4 4-bit numbers and produce a 16 bit result. The maximum result of the operation A + B + (C * D) where A, B, C and D are  4-bit numbers is exactly (2^8)-1 - the maximum 8-bit number which would fit in nicely with your requirement.
0
 
LVL 22

Expert Comment

by:grg99
ID: 11925243
"an ALU" is a pretty broad description...

A 4-bit ALU is just like a 1-bit ALU, only 4 times wider and with some carry wires added.

A 1-bit ALU probably takes in TWO 1-bit inputs and generates a 1-bit output and a carry.  Since it's a "ALU" it probably should do at least add, subtract, and, and or.


For the add part, you need a 1-bit adder with carry.  That's a XOR gate for the output, an AND gate for the carry.

For subtract, you just need a way to negate the second input bit. That's another XOR gate.

For the AND and OR parts, you need an AND gate and an OR gate.

To make the function selectable, let's say you have a 2-bit op-code coming in:

00 ADD
01 SUB
10 AND
11 OR

You use the FIRST bit to select enable either the arithmetic section or the logical section.

You use the second bit to enable the add/and versus the sub/or.

Pretty easy, jsut a few gates, with the outputs either gated together, or tri-stated to the output.

0

Featured Post

How to improve team productivity

Quip adds documents, spreadsheets, and tasklists to your Slack experience
- Elevate ideas to Quip docs
- Share Quip docs in Slack
- Get notified of changes to your docs
- Available on iOS/Android/Desktop/Web
- Online/Offline

Join & Write a Comment

Suggested Solutions

Complex Numbers are funny things.  Many people have a basic understanding of them, some a more advanced.  The confusion usually arises when that pesky i (or j for Electrical Engineers) appears and understanding the meaning of a square root of a nega…
We are taking giant steps in technological advances in the field of wireless telephony. At just 10 years since the advent of smartphones, it is crucial to examine the benefits and disadvantages that have been report to us.
Illustrator's Shape Builder tool will let you combine shapes visually and interactively. This video shows the Mac version, but the tool works the same way in Windows. To follow along with this video, you can draw your own shapes or download the file…
In this tutorial you'll learn about bandwidth monitoring with flows and packet sniffing with our network monitoring solution PRTG Network Monitor (https://www.paessler.com/prtg). If you're interested in additional methods for monitoring bandwidt…

760 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

21 Experts available now in Live!

Get 1:1 Help Now