Digital Logic and

Microprocessors

By

Milind A. Pelagade

ME (Production)

Govt. College of Engineering,

Aurangabad.

Number System

Number System Radix(Base)

Binary 0,1

Decimal 0,1,2,3,4,5,6,7,8,9

Octal 0,1,2,3,4,5,6,7

Hexadecimal 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F

Decimal System :- The decimal system is composed of 10 numerals

or symbols. These 10 symbols are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9; using

these symbols as digits of a number, we can express any quantity. The

decimal system, also called the base-10 system because it has 10

digits.

410 310 210 110 010 110 210 310 410 510

• Binary System:- In the binary system, there are only two symbols or

possible digit values, 0 and 1. This base-2 system can be used to

represent any quantity that can be represented in decimal or other

number system.

42 32 22 12 02 12 22 32 42 52

• Octal NumberSystem:-The octal number system has

a base of eight, meaning that it has eight possible digits:

0,1,2,3,4,5,6,7.

48 38 28 18 08 18 28 38 48 58

• Hexadecimal Number Sytem:- The hexadecimal system uses base 16. Thus, it has 16 possible digit symbols. It uses the digits 0 through 9 plus the letters A, B, C, D, E, and F as the 16 digit symbols.

416 316 216 116 016 116 216 316 416 516

Logic Gates • Basically Logic gates are Building Blocks of Digital Electronic

Circuits.

• Basic NOT Gate • Circuit with One input

NOT P=A A P

A P

0 1

1 0

• Circuits with two Inputs

AND P = X.Y

OR P= X+Y

xy

xy

x+yxy

X Y P

0 0 0

0 1 0

1 0 0

1 1 1

X Y P

0 0 0

0 1 1

1 0 1

1 1 1

Basic AND and OR

Basic NAND and NOR

• Circuits with two Inputs

NAND P = X.Y

NOR P= X+Y

xy

xy

x+yxy

X Y P

0 0 1

0 1 1

1 0 1

1 1 0

X Y P

0 0 1

0 1 0

1 0 0

1 1 0

Basic XOR and XNOR

• Circuits with two Inputs:

XOR P = X Y

XNOR P = A B

xyxy

A

BP

X Y P

0 0 0

0 1 1

1 0 1

1 1 0

A B P

0 0 0

0 1 1

1 0 1

1 1 0

Boolean Algebra Boolean Algebra

-Algebra with Binary(Boolean) Variable and Logic Operations.

-Boolean Algebra is useful in Analysis and Synthesis of Digital Logic

Circuits.

-Input and Output signals can be represented by Boolean Variables.

-Also, Function of the Digital Logic Circuits can be represented by

Logic Operations, i.e., Boolean Function(s).

-From a Boolean function, a logic diagram can be constructed using

AND, OR, and I .

Truth Table

The most elementary specification of the function of a Digital Logic

Circuit is the Truth Table.

- Table that describes the Output Values for all the combinations

of the Input Values, called MINTERMS.

- n input variables → 2n minterms

Boolean Algebraic Laws

(A.B).C = A.B.C = A.(B.C) Associative

A.(B + C) = A.B + A.C

A + (B.C) = (A + B).(A + C) Distributive

A . B = B . A

A + B = B + A Commutative

A . 0 = 0 A . 1 = A

A + 0 = A A + 1 = 1

Operating with logic 0 and logic 1

A . A = 0

A + A = 1 Complementary

A . A = A

A + A = A Tautology (Idempotent)

KARNAUGH MAPS

• Named for the American electrical engineer Maurice Karnaugh

• Karnaugh maps provide an alternative way of simplifying logic circuits.

• Instead of using Boolean algebra simplification techniques, you can transfer logic values from a Boolean statement or a truth table into a Karnaugh map.

• The arrangement of 0's and 1's within the map helps you to visualise the logic relationships between the variables and leads directly to a simplified Boolean statement.

• Karnaugh maps, or K-maps, are often used to

simplify logic problems with 2, 3 or 4 variables. No of Cells = 2n

(where n is a number of variables)

For the case of 2 variables, we form a map consisting of 22=4 cells as shown in Figure

BA+ BA +

BA+ BA +

00 10

01 11

BA+ BA +

BA+ BA +

0 2

1 3

BA

BA AB

BA

A

B 0 1

0

1

A

B 0 1

0

1

A

B 0 1

0

1

• 3 variables Karnaugh map

NO of Cells = 23=8

AB

C 00 01 11 10

0

1

CBA CBA CAB CBA

CBA BCA ABC CBA

0 2 6 4

5 3 1 7

• 4 variables Karnaugh map

AB

CD 00 01 11 10

00

01

11

10

5

3

1

7

6 2

0 4

9

15

13

11

10 14

12 8

NO of Cells = 23=16

SEQUENTIAL LOGIC SYSTEM

•When a System requires an output which depends on earlier values of

inputs a sequential logic system is required.

•A sequential circuit consists of a feedback path, and employs some

memory elements.

•Sequential circuit = Combinational logic + Memory Elements

Combinational

logic

Memory

elements

Combinational

outputs Memory outputs

External inputs

The FLIP-FLOP

• The Flip-Flop is a basic memory element which is made

up of assembly of Logic gates.

• Output changes state at a specified point on a triggering

input called the clock.

• Change state either at the positive edge (rising edge) or at

the negative edge (falling edge) of the clock signal.

Positive edges Negative edges

Clock signal

S-R Flip-Flop S-R flip-flop: on the triggering edge of the clock

pulse,

S=HIGH (and R=LOW) a SET state

R=HIGH (and S=LOW) a RESET state

both inputs LOW a no change

both inputs HIGH a invalid

Characteristic table of S-R flip-flop:

S Q

Q' R

S R CLK Q(t+1) Comments

0 0 X Q(t) No change

0 1 0 Reset

1 0 1 Set

1 1 ? InvalidCLK

S Q

CLK

R Q

Symbol Of SR Flip-

Flops

J-K Flip Flop

• For many applications the indeterminate state that occurs with SR

Flip-Flops when S=1 and R=1 is invalid then another form of Flip

Flop is used called J-K Flip Flop.

• The main difference between SR and JK Flip Flops is that there is no

Invalid state in JK Flip Flop.

• Include a toggle state.

J=HIGH (and K=LOW) a SET state

K=HIGH (and J=LOW) a RESET state

both inputs LOW a no change

both inputs HIGH a toggle

J Q

Q'

CLK

K

J-K flip-flop

J K CLK Q(t+1) Comments

0 0 Q(t) No change

0 1 0 Reset

1 0 1 Set

1 1 Q(t)' Toggle

Q J K Q(t+1)

0 0 0 0

0 0 1 0

0 1 0 1

0 1 1 1

1 0 0 1

1 0 1 0

1 1 0 1

1 1 1 0

Characteristics Table:-

J Q

CLK

K Q

D Flip-flop

Basically a clocked SR Flip Flop or JK Flip Flop with D input

directly connected to S or J Input and via NOT gate to R or K

gate.

D flip-flop: single input D (data)

D=HIGH a SET state

D=LOW a RESET state

S

C

R

Q

Q'

CLK

D

D CLK Q(t+1) Comments

1 1 Set

0 0 Reset

REGISTERS • A register is a set of memory elements and is used to hold

information till it is needed.

• It can be done by using set of Flip Flops.

• The register using D Flip Flop is shown below:

* After occurrence of negative-going

transition

Q1 =

X*

D

CLK

Q

Q'

Q2 =

Y*

D

CLK

Q

Q'

Q3 =

Z*

D

CLK

Q

Q'

Combinational

logic circuit

Transfer

X

Y

Z

• When Load signal is 0, NO clock input occurs to

D Flip Flops and so no change occurs to the

state of Flip Flops.

• When Load signal is 1 then the input can

change the states of Flip Flops.

• As long as load signal is 0 the FLIP FLOPS will

HOLD their OLD STATE VALUES.

Microprocessors

• A computer is a programmable machine that receives

input, stores and manipulates data/Information, and

provides output in a useful format.

• The microprocessor can be programmed to perform

functions on given data by writing specific instructions

into its memory.

– The microprocessor reads one instruction at a time,

matches it with its instruction set, and performs the

data manipulation specified.

– The result is either stored back into memory or

displayed on an output device.

Basic Components of

Microprocessor system

Microprocessor system has folllowing three parts

1. CPU - Central Processing Unit:-

the portion of a computer system that carries out the

instructions of a computer program

2. Input/output (I/O):-

refers to the communication between a computer and

the outside world possibly a human, or another

information processing system.

3. Memory:-

physical devices used to store data or programs

(sequences of instructions) on a temporary or

permanent basis.

The MICROPROCESSOR

• Generally referred to as Central Processing Unit (CPU).

• It is that part which fetches, decodes and executes an

information

• The following figure illustrates block diagram of

microprocessor

ALU

Register

Section

Control and timing section

Address bus

Data bus

Control bus

• Arithmetic and logic unit (ALU) • The component that performs the arithmetic and logical

operations

• It is responsible for performing data manipulation.

• Register

• used to temporarily store data or program codes until they

are sent to the ALU or to the control section or to memory.

• The number of registers are different for any particular

CPU and the more register a CPU have will result in easier

programming tasks.

• Registers are normally measured by the number of bits they

can hold, for example, an "8-bit register" or a "32-bit register".

• Control Unit

• The circuitry that controls the flow of information through the

processor, and coordinates the activities of the other units

within it.

• On a regular processor, the control unit performs the tasks of

fetching, decoding, managing execution and then storing

results.

• Operations involving the microprocessor are reckoned in terms

of no of cycles they take.

Types of Registers

• Accumulator Register:-

• a register in which intermediate arithmetic and logic results

are stored.

• example for accumulator use is adding a list of numbers.

– The accumulator is initially set to zero, then each number

in turn is added to the value in the accumulator.

– Only when all numbers have been added is the result held

in the accumulator written to main memory or to another,

non-accumulator, CPU register.

• Status Register or Condition Code or

Flag Register

• Contains information about result of process carried out in

ALU.

• Contains individual bits with each bit having special

significance. The Bits are called Flags.

• The status of latest bit indicated by each flags being set or

reset to indicate specific status.

FLAG SET (i.e. 1) RESET (i.e. 0)

Z Result is zero Result is not zero

N Result is Negative Result is not Negative

C Carry is generated Carry not Generated

V Overflow Occurs Overflow Do not Ouccr

I Interrupt ignored Interrupt processed

• Program Counter Register(PC) or Instruction Pointer (IP)

• a 16 bit register, used to store the next address of the

operation code to be fetched by the CPU.

• Not much use in programming, but as an indicator to

user only.

• Purpose of PC in a Microprocessor

– to store address of tos (top of stack)

– to store address of next instruction to be executed.

– count the number of instructions.

– to store base address of the stack.

• Memory Address Register (MAR) • Contains Address of data.

• Example:-

1. consider summing of two numbers,

2. MAR is loaded with address of first number. The data

at address is moved to accumulator.

3. The memory address of second number is then loaded

into MAR.

4. The data at this address is then added in accumulator.

5. The result is then stored in a memory location

addressed by MAR.

• Instruction Register (IR)

• Stores an Instruction.

• After fetching an instruction from memory via data Bus,

the CPU stores it in the form of instruction register.

• After each such fetch, the microprocessor increments

program counter by one with the result that the program

counter points to next instruction to be fetched.

• The instruction can then be decoded and used to execute

operation. This called FETCH EXECUTE cycle.

• General Purpose Register

• May serve as temporary storage for data and address and

used in operations involving transfer between other

registers.

• Stack Pointer Register

• The contents of this register form an address which

defines the top stack of in RAM.

• It is a special area of the memory in which program

counter values can be stored when a subroutine part of a

program is being used i.e. pushing the return address on

a jump, and retrieving it after the operation is complete

to come back to its original location.

INTEL 8085A

Development of earlier 8080 processor.

Six general purpose 8-bit registers: B, C, D, E, H, L

They can also be combined as register pairs to

perform 16-bit operations: BC, DE, HL

Registers are programmable (data load, move, etc.)

Accumulator

Single 8-bit register that is part of the ALU !

Used for arithmetic / logic operations – the result is

always stored in the accumulator.

The internal architecture of the 8085 CPU is capable of performing the

following operations:

Store 8-bit data (Registers, Accumulator)

Perform arithmetic and logic operations (ALU)

Test for conditions (IF / THEN)

Sequence the execution of instructions

Store temporary data in RAM during execution

Microcontrollers • Microcontroller is an integration of a

microprocessor with memory and Input-

Output interfaces.

• It has pins for external connections of input

and output, power, clock and control signals.

• The pins for input and output are grouped

into units called input-output ports.

• To transmit data there are lines on the ports

for 8-bit – Single port

for 16-bit- Double Ports

Block diagram of Microcontroller

Basic I/O Concepts

• Peripherals such as LEDs and keypads are essential components of microcontroller-based systems

• Input devices – Provide digital information to an MPU (Memory

protection Unit).

– Examples: switch, keyboard, scanner, and digital camera

• Output devices – Receive digital information from an MPU.

– Examples: LED, seven-segment display, LCD, and printer

• Devices are interfaced to an MPU using I/O ports.

I/O Interfacing

Industrial Applications of

Microcontroller 1. Temperature Measurement System

2. Washing machine

Digital-to-Analog Conversion

• When data is in binary form, the 0's and 1's may be of several forms such as the TTL form where the logic zero may be a value up to 0.8 volts and the 1 may be a voltage from 2 to 5 volts.

• The data can be converted to clean digital form using gates which are designed to be on or off depending on the value of the incoming signal.

Analog-to-Digital Conversion

• The basic principle of operation is to use the

comparator principle to determine whether or

not to turn on a particular bit of the binary

number output.

• It is typical for an ADC to use a digital-to-

analog converter (DAC) to determine one of

the inputs to the comparator

Elements(Hardware) in Mechatronics

System

• Principle elements of Mechatronics System are

• Mechanical Elements:-

Refers to Mechanical Structure, Mechanism, Thermo Fluid,

Hydraulic aspects of Mechanical system.

• Electro-Mechanical Elements:-

Refers to Sensors And Actuators

• Electrical / Electronic Elements:-

Refers to electrical components like capacitor, Inductor,

transformer, Circuits etc.

• Control interface/Computing hardware Elements:-

Refers to Analog-to-Analog convertor, Digital-to-Analog

Convertor, I/P-O/P system, Counters, Timers etc.

• Computer:-

Refers to Hardware/Software utilized to perform Computer

aided dynamics system analysis, Optimization, Design and

Simulation etc.