PROJECT REPORT ON 4-BIT ARITHMETIC AND LOGIC UNIT (ALU) USING ADDERS SUBMITTED BY MOHAMMED AZHER KHAN ( 04-08-4018 ) MOHAMMED AZHARUDDIN ( 04-08-4024 ) ON COMPLETION OF TWO WEEK WORKSHOP ON DIGITAL AND ANALOG VLSI DESIGN CO-ORDINATOR Mr. ARIFUDDIN SOHEL Assoc. Prof., ECED MJCET DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING MUFFAKHAM JAH COLLEGE OF ENGINEERING AND TECHNOLOGY
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PROJECT REPORT ON
4-BIT ARITHMETIC AND LOGIC UNIT (ALU) USING ADDERS
SUBMITTED BY
MOHAMMED AZHER KHAN ( 04-08-4018 )
MOHAMMED AZHARUDDIN ( 04-08-4024 )
ON COMPLETION OF TWO WEEK WORKSHOP ON
DIGITAL AND ANALOG VLSI DESIGN
CO-ORDINATOR
Mr. ARIFUDDIN SOHEL
Assoc. Prof., ECED
MJCET
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
MUFFAKHAM JAH COLLEGE OF ENGINEERING AND TECHNOLOGY
ABSTRACT
The aim of this project was to create a four-bit arithmetic logic unit. This
ALU was to take two four bit numbers and perform the following
operations on them - add, subtract,detect equality,or and exclusive-or
function. The ALU has 4 full adders and eight 2:1 multiplexers.
INTRODUCTION
This project was done in a structural manner. The implementation of the 4-bit ALU circuit
was done on Tanner Tools version 12.6 . We have laid out this report so that the information
portrayed will be easy to verify and comprehend. We have attempted to show all the
operations of ALU by giving all the possible inputs to the circuit .And the waveforms of both
inputs and corresponding outputs are recorded .
This should allow the viewer to simply hold a sheet of paper over the waveform output and
see the explanation of the inputs and results.
DESCRIPTION
IMPLEMENTING 4-BIT ALU USING ADDERS
An arithmetic and logical operaions unit(ALU) must,obviously be able to add two binary
numbers (A+B), and must also be able to subtract (A-B).
From the point of view of the logical operations it is essential to be able to And two binary
words (A.B). It is also desirable to Or (A+B) and perhaps also detect Equality, and of course
we also need an Exclusive-Or function.
Substraction by adder is an easy operation provided that the binary numbers A and B are
presented in twos complement form. In this case, to find the difference A-B it is only
necessary to complement B (exchange for 0 and vice versafor all the bits of B), add 1 to the
number thus obtained , then add tis quantity to A using the standard assition process
discussed earlier.The output of the adder will then be required difference in twos
complement form.Note that the complement facility necessary for substraction also serve to
form the logical complement (which is indeed exchanging 0 and 1 and vice-versa).
It is highly desirable to keep the architecture of ALU as simple as possible, and it
would be nice if the adder could be made to perform logical operations as readily as it
performs substraction.
In order to examine this possibility, consider the standard adder equation set.
Sum S=H’kCk-1 + HkC’k-1
New carry Ck=AkBk + HkCk-1
Where Half sum H=A'kBk + AkB’k
Consider, first the sum output if Ck-1 is held at logical 0, then
Sk= Hk.1 + H’k. =Hk
that is Sk=Hk=AkBk + AkBk ---------An Exclusive-Or operation
Now , hold Ck-1 a logical 1, then
S’k =Hk.0 + H’k.1 = H’k
that is Sk =H’k=A’kB’k + AkBk ---------An Exclusive-Nor (Equality)
operation
Next,consider the carry output of each element, first if Ck-1 is held at logical 0.
Then Ck=AkBk + Hk.0----------An And operation
Now if Ck-1 is held at logical 1, then
Ck = AkBk + Hk.1 = AkBk + A’k Bk +Ak.B’k
Therefore Ck= Ak + Bk --------------An Or operation
Thus it may be seen that the suitable switching of the carry line between adder elements will
give the ALU logical functions.A possible arrangement of the adder elements for both the
arithmetic and logic fuctions is suggested in the diagram as shown.
BLOCK DIAGRAM
T-SPICE PROGRAM
* SPICE export by: SEDIT 12.60
* Export time: Fri Jul 16 15:27:57 2010
* Design: azhar
* Cell: alu_4bit
* View: view0
* Export as: top-level cell
* Export mode: hierarchical
* Exclude .model: no
* Exclude .end: no
* Expand paths: yes
* Wrap lines: no
* Root path: D:\azhar
* Exclude global pins: no
* Control property name: SPICE
********* Simulation Settings - General section *********
.probe
.option probev
.option probei
.option probeq
.lib "C:\Documents and Settings\admin.MJCET-50B89CA38\My