lecture 10 alu and control unit design presented by dr. shazzad hosain asst. prof. eecs, nsu

Lecture 10ALU and Control Unit Design

Presented ByDr. Shazzad Hosain

Asst. Prof. EECS, NSU

ALU Design• Arithmetic Unit• Logic Unit

4-bit parallel adder

Cin

Cout

x3

x2

x1

x0

y3

y2

y1

y0

X

Y

Arithmetic Unit

Ff3

f2

f1

f0

A3

A2

A1

A0

B3

B2

B1

B0

Arithmetic UnitLets take the following two operations

F = X + Y F = X – Y

4-bit parallel adder

Cin

Cout

XF

Y

S0

01

= X + Y + 0= X + (-Y) = X + (Y + 1) = X + Y + 1

4-bit parallel adder

MUX0

1

MUX0

1

MUX0

1

MUX0

1

Cin

Cout

x3

x2

x1

x0

y3

y2

y1

y0

S0

Ff3

f2

f1

f0

Block Diagram of Arithmetic Unit

Arithmetic Unit

4

4

X

Y

4F

S0

Logic UnitS0 Operation

0 X AND Y

1 X XOR Y

Block Diagram of Logic Unit

LogicUnit

4

4

X

Y

4G

S0

Block Diagram of ALU

LogicUnit

4

4X

Y

4 G

S0

Arithmetic Unit

4

4

X

Y

4 F

S0

4

Mul

tiple

xer 4

Z

S1

Design of the Control Unit

• Two types of control unit design– Hardwired Control Design– Micro-programmed Control Unit Design

Basic Concepts Transfer to

Transfer 14th bit of to 1st bit of

Transfer to if E is enabled

Multiplication Using Addition

Microprocessor speed depends on bus architecture

Bus Architecture

• Three types of bus architectures– Single-bus architecture– Two-bus architecture– Three-bus architecture

Single Bus Architecture

Two-bus Architecture

• One of the main task of control unit is to sequence a set of operations properly

• Use a ring counter to implement this

Timing Signals

Hardwired Control Design• Eight Steps to follow

Step 1: Derive the Flow ChartStart

Stop

R 0M Multiplicand via inbus

Q Multiplier via inbus

R R + MQ Q – 1

Q=0

Outbus R

no

yes

Step 2: Obtain register transfer description

Step 3: Specify processing hardware along with various components

Step 4: Complete the design of the processing section

M

L

CD

C0: R ← 0C1: M ← inbusC2: Q ← inbusC3: F ← r + lC4: Q ← Q – 1 C5: outbus ← RC6: R ← F

R

CL

DQ

LD

C

4 4

C0

44

4-bitadder

F

C1 C2

C3

C4

C5

C6

Z

Step 5: Determine the block diagram of the controller

0

1

2

3

4

5

6

References

• Chapter 7, Fundamental of Digital Logic and Microcomputer Design – by M. Rafiquzzaman