Digital Fundamentals and Computer Architecture

Unit:1 Number System and Arithmetic circuits: Decimal, Binary, Octal, Hexadecimal – Binary

addition, Multiplication, Division – Floating point representation, Complements, BCD, Excess3,

Gray Code. Arithmetic Circuits: Half adder, Full adder, Parallel binary adder, BCD adder, Half

subtractor, Full subtractor, Parallel binary subtractor - Digital Logic: The Basic Gates – NOR,

NAND, XOR Gates.

Unit:2 Combinational Logic Circuits: Boolean algebra – Karnaugh map – Canonical form

Construction and properties – Implementations – Don’t care combinations - Product of sum,

Sum of products, Simplifications. Sequential circuits: Flip-Flops: RS, D, JK, and T - Multiplexers –

Demultiplexers – Decoder Encoder – Shift Registers-Counters.

Unit:3 Input – Output Organization: Input – output interface – I/O Bus and Interface – I/O Bus

Versus Memory Bus – Isolated Versus Memory – Mapped I/O – Example of I/O Interface.

Asynchronous data transfer: Strobe Control and Handshaking – Priority Interrupt: Daisy-

Chaining Priority, Parallel Priority Interrupt. Direct Memory Access: DMA Controller, DMA

Transfer. Input – Output Processor: CPU-IOP Communication.

Unit:4 Memory Organization: Memory Hierarchy – Main Memory- Associative memory: Hardware

Organization, Match Logic, Read Operation, Write Operation. Cache Memory: Associative, Direct, Set-

associative Mapping – Writing into Cache Initialization. Virtual Memory: Address Space and Memory

Space, Address Mapping Using Pages, Associative Memory, Page Table, Page Replacement.

Unit:5 Case Studies 6 hours CASE STUDY: Pin out diagram, Architecture, Organization and addressing

modes of 80286- 80386-80486-Introduction to microcontrollers.

Unit:6 Contemporary Issues 2 hours Expert lectures, online seminars - webinars

Text Book(s)

1 Digital principles and applications, Albert Paul Malvino, Donald P Leach, TMH, 1996.

2 Computer System Architecture -M. Morris Mano , PHI.

3 Microprocessors and its Applications-Ramesh S. Goankar

Reference Books

1 Digital Electronics Circuits and Systems, V.K. Puri, TMH.

2 Computer Architecture, M. Carter, Schaum‘s outline series, TMH.

Prepared By Dr.D.UMA MAHESWARI ASSISTANT PROFESSOR

DEPARTMENT OF COMPUTER SCIENCE GOVERNMENT ARTS AND SCIENCE COLLEGE, VALPARAI

UNIT INumber System and Binary Codes: -Decimal, Binary, Octal, Hexadecimal– Binary addition, Multiplication, Division– Floating point representation, Complements, BCD, Excess3, Gray Code.Arithmetic Circuits:-Half adder, Full adder,-Parallel binary adder ,Parallel binary Subtractor -BCD adder, -Half Subtractor, Full SubtractorDigital Logic: The Basic Gates NOR, NAND, XOR Gates

• NUMBER SYSTEM AND BINARYCODES:

– DECIMAL SYSTEM 0,1……9radix or base 10

– BINARY SYSTEM-0,1 radix or base 2

– OCTAL SYSTEM 0,1…..7– radix or base 8

– HEXADECIMAL SYSTEM 0,1…..15– 10-A– radix or base 16

Digital System

• In digital system the terms bit, nibble, and byteare frequently used.

• Bit is an app of Binary digit.

• Bit is the basic unit of memory and the twobinary digits are 0 and 1.

• Byte is a string of 8 bitseg:10011011,01010111 etc.

• Nibble is a string of 4 bits such as 1101,1011etc.

• In digital systems a group of bits which is stored,operated and moved around is called a word.

• One word consists of 16 bits or two bytes such as01110100,01010101.

• The first 8 bits represents upper byte and last 8 bitsrepresents the longer byte.

• Chuncking means replacing a longer string of databy a shorter one.

• A Program is a sequence of instructions that tells the

computer,how to process the data. It is also known as

software.

• The combination of electronic,magnetic,and

mechanical devices of a computer is called

hardware.

Integrated circuits or chips• Digital circuits - are constructed using Ics due to the

advantages of reduction in size, low cost, reducedpower consumption, higher operating speed, higherreliability against failure thus less prone to repairs.

• Small Scale Integration (SSI): upto 10 logic gates ina single chip.

• Medium Scale Integration (MSI): 10 to 100 gatesper chip .

• Large Scale Integration (LSI):

100 to 10000 gates per chip.

• Very Large Scale Integration (VLSI):

-More than 10000 gates but less than 100000 gates perchip.

• Ultra Large Scale Integration (ULSI):

-100000 or more gates per chip.

Convert Decimal to binary

0s and 1s – base or radix is 2

332

2

2

2

2

16 -1

8 - 0

4 - 0

2 - 0

1 - 0

(100001)2

Dibble-Dabble method

1.Convert Decimal to binary

a.(33)10 b.(1993)10

Convert Decimal to Octal

0,1,2,…7– base or radix is 8

338

4 -1

(41)8

Convert Decimal to HexaDecimal

0,1,2,…15– base or radix is 16

10-A ,11-B,12-C,13-D,14-E,15-F

3316

2 -1

(21)16

HOME WORK

• a.(1993)10

• b. (1996)10

• c. (247)10

• d. (624)10

• E.((510)10

Rules0+0=00+1=11+0=1

1+1=10 ie.. 0 with carry over of 1

Rules0-0=01-0=11-1=0 0-1=1

ie.. 1 with borrowof 1

BINARY ADDITION• 100101 + 100101

Sol:

A) 100101 C)1100.011+

+ 100101 1011.011

1001010 Ans ???

B) 1011.01

+ 1001.11

10101.00 Ans

BINARY SUBTRACTIONa)1 10.01-100.1

Sol:

A) 110.01

- 100.10

001 . 11 Ans

A) 11.01111- 10.01001

???

COMPLEMENTS

BCD Adder• *BCD abbreviated as Binary Coded Decimal.• *Each decimal digit of any number lies between 0 to 9 will

be allowed in the BCD form,other combinations ie morethan 9 like 1010,1011,1100,1101,1110,1111(10,11,12,13,14,15)are not possible in BCD forms and arecalled forbidden groups.

• *Difficulty arises when the sum of the two numbers toadded is more than 9

• Ex:9+3=12 in the binary addition we obtain 12 in binaryform 1100.

• *But it is allowed in the BCD form.• *To allow BCD we have to add 6 (=0110)• Ex:For adding 9 (=1001)+3(=0011) to the sum is

10010=0001 0010 which is the correct answer in BCD form.

Arithmetic Circuits-Half adder, Full adder,

-Parallel binary adder ,Parallel binary Subtractor -BCD adder,

-Half Subtractor, Full Subtractor

HALF SUBTRACTOR

It is a multiple output combinational logic network which

Subtracts two bits of binary data bits producing a different bit d and a borrow bit b as the two output signals.

A

B

d(difference)Half

Subtractor

Input Output

Block

Diagram:

b (borrow out)

HALF SUBTRACTOR

Karnaugh Map:

Logic

Diagram:

This Logic Diagram using an XOR gate,a NOT gate and an AND gate .

Differnece bit output of a half subtractor is Exclusive OR(XOR) of the two inputs A and B ie., d=A B.

The combinational logic network which subtracts threeinputs and two outputs. The two outputs produced are thedifferent bit d and a borrow bit b as the two output signals.

FULL SUBTRACTOR

Logic

Symbol:

Logic

Diagram:

A

B

Di (difference)

B0 (borrow out)

Full

Subtractor

Input Output

Bin

A

B

Di

B0H. S.

H. S.Bin

• Parallel binary adder

• We can add two binary numbers .Let the two binary number to be added be A3 A2 A1 A0 and B3 B2 B1 B0

and their sum C4 S3 S2 S1 S0 where C4 is the final carry.

Example to perform Binary addition of 1110 and 1011.Sol: The full adder on the right most is a half adder and it produces asum bit of 1 and a carry bit of 0.The second adder which is a full adderas it ha three in outs produce a sum bit of 0 and carry bit of 1.The fourthand last adder which is again a full adder produces a sum bit of 1 and acarry output bit of 1,as it has three inputs which are all1. the binaryadder output is 11001 by adding the 1110 and 1011.

Parallel binary Subtractor

A Parallel Subtractor is a digital circuit capable of finding thearithmetic difference of two binary numbers that is greaterthan one bit in length by operating on corresponding pairs ofbits in parallel. The parallel Subtractor can be designed inseveral ways including combination of half and full Subtractor,all full Subtractor or all full adders with subtrahendcomplement input

Logic Gates

In Boolean Algebra, there are three basic operations, whichare analogous to disjunction, conjunction, and negationin propositional logic. Each of these operations has acorresponding logic gate. Apart from these there are a fewother logic gates .

AND gate(.) – The AND gate gives an output of 1 if boththe two inputs are 1, it gives 0 otherwise.

OR gate(+) – The OR gate gives an outputof 1 if either of the two inputs are 1, itgives 0 otherwise.

NOT gate(‘) – The NOT gate gives an output of 1 input is 0 and vice-versa.

NAND gate()- The NAND gate (negated AND) gives an output of 0 if both inputs

are 1, it gives 1 otherwise.

NOR gate()- The NOR gate (negated OR) gives an output of 1 if both inputs are 0, it

gives 0 otherwise.

NOR gate()- The NOR gate (negated OR) gives an output of 1 if both inputs are 0, it gives 0 otherwise.

XNOR gate()- The XNOR gate (negated XOR) gives an output of 1 both inputs are same and 0 if both are different.

UNIT II

Combinational Logic Circuits:

-Boolean algebra

– Karnaugh map

– Canonical form 1

Construction and properties

– Implicants

– Don‘t care combinations

- Product of sum,

-Sum of products

- simplifications

2

• Understand the relationship between Boolean logic and digital

computer circuits

• It can applied in digital circuit Designing and logical Derivations

will understand rules and laws.

• .Learn how to design simple logic circuits.

• Understand how digital circuits work together to form complex

computer systems.

• It is the branch of algebra in which the values of the variable are the truth values true or false, usually denoted 1 and 0 respectively.

• Boolean Algebra was introduced by George Boole in his first book ”The Mathematicla Analysis of Logic “(1987).

• Boolean algebra has been fundamental in the development of digital electronics and is provided for in all modern programming language

• Variable used can have only two values.

– Binary 1 for HIGH.

– -Binary 0 for LOW

BOOLEAN ALGEBRA

• Boolean algebra is a mathematical system for the manipulation of variables that can have one of two values.– In formal logic, these values are “true” and “false.”– In digital systems, these values are “on” and “off,” 1 and 0,

or “high” and “low.”

• Boolean expressions are created by performing operations on Boolean variables.– Common Boolean operators include AND, OR, and NOT.

• In Boolean Algebra here satisfying four properties for any elements.

i) a+b=b+a and a.b=b.a –Commutative Law

ii) a+1=1,a.1=a and a+0=a,a.0=0 –Identity Element

iii) a.(b+c)=a.b+a.c and- Demorgan’s Law

a+(b.c)=a+b.a+c

iv) a+a’=1 and a.a’=0- Complement

4

Karnaugh Map

• The map method first proposed and invented by E.W.Veitch and later modified by M.Karnaugh ,provides a simpleset procedure for minimizing the switch function.

Cont..

• Karnaugh maps (K-maps) are made up ofsquares.Here each squares represents oneterm.

• The k-map is a systematic method forcombining the terms and determining minimalexpression.Each n variable map consists of 2n

cells or squares.• Thus a three variable map will consist of 23 or

8 cells or four-variable map will consist of 24

or 16 cells(squares).

6Boolean Algebra PJF - 6

Three-Variable Map

6Boolean Algebra PJF - 6

Three-Variable K-Map

ee-Variable MapA Three –variable k-map for switching functionf(A,B,C).It has 8 cells or squares.The first square has AB value of function=00 andC value=0,thus it represents the binary numberABC=000,which is equal to 0 in the decimalsystem.

Four-Variable Map

7

The Figure shows Four Variable k-mapfor a switching function f(A,B,C,D).It has16 cells and squares. Each square, hereagain represents a particular decimalvalue of th function.

Canonical Form 1

• We need to consider formal techniques for the simplification of Boolean functions.– Identical functions will have exactly the same

canonical form.

– Minterms and Maxterms

– Sum-of-Minterms and Product-of- Maxterms

– Product and Sum terms

– Sum-of-Products (SOP) and Product-of-Sums (POS)

8

9

Literal: A variable or its complementProduct term: literals connected by •Sum term: literals connected by +Minterm: a product term in which all thevariables appear exactly once, eithercomplemented or uncomplemented.Maxterm: a sum term in which all thevariables appear exactly once, eithercomplemented or uncomplemented.

Definitions

Minterm

• Represents exactly one combination in the truth table.

• Denoted by mj, where j is the decimal equivalent of the minterm’s corresponding binary combination (bj).

• A variable in mj is complemented if its value in bj is 0, otherwise is uncomplemented.

• Example: Assume 3 variables (A,B,C), and j=3. Then, bj = 011 and its corresponding mintermis denoted by mj = A’BC

10

• Represents exactly one combination in the truth table.

• Denoted by Mj, where j is the decimal equivalent of the maxterm’s corresponding binary combination (bj).

• A variable in Mj is complemented if its value in bj is 1, otherwise is uncomplemented.

• Example: Assume 3 variables (A,B,C), and j=3. Then, bj

= 011 and its corresponding maxterm is denoted by Mj

= A+B’+C’

Maxterm

MAXTERM

Truth Table notation for Minterms and Maxterms

12

Decimal Valu

e

A B C f

0 0 0 0 0

1 0 0 1 1

2 0 1 0 1

3 0 1 1 0

4 1 0 0 1

5 1 0 1 0

6 1 1 0 0

7 1 1 1 1

Ex:1 Find the Sum of Products(SOP) form of Switching function f(A,B,C) ,which is represented by the truth table given below..

From the table it is evidentthat the decimal values forwhich the function f assumes the value ‘1’ are1,2,4,7.Thus the function f(A,B,C) is the sum of theseproduct term ie=(1,2,4,7)

=(1,2,4,7)=001+010+100+111f(A,B,C)=A’B’C+A’BC’+AB’C’+ABCWHICH IS THE PRODUCT OF SOP FORM OFTHE FUNCTION.

f(A,B,C) ,which is represented by the above truth table .

From the truth table ,it is evident that the decimal values for which the function f assumes the value 0 are 0,3,5,6.Thus the functions f(A,B,C) is product of these sum terms.

14

=II(0,3,5,6)=000+011+101+110f(A,B,C)=(A+B+C) (A+B’+C’) (A’+B+C’) (A’+B’+C)WHICH IS THE SUM OF POS FORM OF THE FUNCTION.

Construction and properties

– Implicants

– Don‘t care combinations

- Product of sum,

-Sum of products

- simplifications

The karnaugh map is a modified of the Venn diagram ofthe switching function with four or less variables in thecanonical sum of products form.The switching function, by combining 1 cells into pairs,Quartets or Octets .The variables are represented by 0’s and 1’s .Complemented and uncomplemented variables arerepresented by 0’s and 1’s.If the switching function consist of 2 variables then the k-map has 4 squares.If the switching function consist of 3 variables then the k-map has 8 squares.If the switching function consist of 4 variables then the k-map has 16 squares.

IMPLICANTS• Any group of 1 can be considered as implicants i.e

combining the minterms set are called implicants.– Prime Implicants – Essential implicants

• Prime Implicants It is a largest possible group of 1’s.

• Essential Prime Implicants• In the group at least ,there is single 1 which cannot combine in

otherway.

Example

Don’t Care Combinations

• The combinations for which the value of the function is not specified with certinity are called don’t care combination .

The value denoted by or D on the karnaugh map.

EXAMPLE:8

Example:1

Sequential circuits-Flip-Flops

- RS, D, JK, and T -Multiplexers,Demultiplexers

- Decoder, Encoder -shift register

--Counters

Sequential Circuits• Combinational Logic:

– Output depends only on current input.

• Sequential Logic:

– Output depends not only on current input but also on past input values.

Difference between combinational circuit and sequential circuit

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Synchronous vs. AsynchronousThere are two types of sequential circuits:Asynchronous sequential circuit – These circuit do not use a clock

signal but uses the pulses of the inputs. These circuits are faster thansynchronous sequential circuits because there is clock pulse andchange their state immediately when there is a change in the inputsignal.

Synchronous sequential circuit – These circuit uses clock signal andlevel inputs (or pulsed) (with restrictions on pulse width and circuitpropagation). The output pulse is the same duration as the clockpulse for the clocked sequential circuits. Since they wait for the nextclock pulse to arrive to perform the next operation, so these circuitsare bit slower compared to asynchronous. Level output changesstate.

Synchronous Sequential Circuits:Flip flops as state memory

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The flip-flops receive their inputs from the combinational circuit and also from a clock signal with pulses that occur at fixed intervals of time, as shown in the timing diagram.

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SR Latch (NAND version)

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S

R

Q

Q’

0 00 11 01 1

R S 0

0

1

1

Qn Qn No Change

1 1 Invalid,not allowed

1 0 set0 1 Reset

Qn+1 Q’n+1

Output CommentsInput

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SR Latch with Clock signal

Latch is sensitive to input changes ONLY when C=1

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D Latch OR D FLIP FLOP

• One way to eliminate the undesirable indeterminate state in the RS flip flop is to ensure that inputs S and R are never 1 simultaneously. This is done in the D latch:

D Flip-Flop Table

D Flip-Flop

Input Outputs Comment

D Qn+1 Qn+1 Operation

0 0 1 Reset

1 1 0 Set

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Block Diagram Of Master Slave JK-Flip flop

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•Master Slave JK-Flip flop is a popular way avoiding race

condition or race around problem.

•It is a combination of two clocked latches, the first is called

master and the second is called slave.

•The master is positively clocked and the slave is negatively

clocked implying thereby that when clock is high ,master is

active and slave is inactive.

•When clock is low, master is inactive and slave is active

T Flip-Flop

Flip flop is abbreviated form of Toggle flip-flop here the flip flop changes

state or toggles whenever clock pulse occurs and input T is high.

T flip flop is a single input form of the JK Flip flop and is obtained if both J

and K inputs are tied together

Input Output Comments

T Qn+1 Qn+1

O Qn Qn+1 No changes

I Qn Qn Toggles

What ever may be the present state of the output, when T is high or ’1’ the output

Qn+1 will change or toggle to the complement of the previous output.

Multiplexer also known as Data Selector,It is a combinationallogic circuit which accepts several data inputs and selects onlyone output line.

Multiplexer

Block Diagram of MUX

S1 S0 Y

0 0 I0

0 1 I1

1 0 I2

1 1 I3

Function Table4 to 1 Line Multiplexer

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Here there are four inputs I0, I1, I2, I3 each of which is applied to

one input of each of the four AND gates.

These inputs are transmitted to the output according to four possible

combinations of two select inputs s1 and s0.

The outputs of all the AND gates are applied to a single OR gate,

which gives a one line output.

The size of the multiplexer is given by 2n to 1 line, where 2n stands

for the number of its output lines, and n stands form number of

selection lines or select inputs.

Applications:

Multiplexer find wide variety of applications in digital systems. The

main applications of multiplexers in digital systems are data routing,

data selection, parallel to serial conversion, operation sequencing,

waveform generation and logic function generation.

Demultiflexer

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A Demultiflexer ,also known as data distributor ,It takes a single input and transmits information

on one of the 2n possible output lines.

From the above Truth table, we can directly write the Boolean functions for each output as

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DECODERDecoder is a combinational circuit that has ‘n’ input lines and maximum of 2n output lines.

Let 2 to 4 Decoder has two inputs A1 & A0 and four outputs Y3, Y2, Y1 & Y0. The block diagram

of 2 to 4 decoder is shown in the following figure.

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Decoders may be designed for any of the codes by using gates and also it is possible to display

the letters of the alphabet. Light emitting diodes are mostly used as light sources for the read

out display.Encoders

An Encoder is a reverse operation of decoder .It has 2n or less input lines and n output lines.

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Shift Registers

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Serial In − Serial Out SISO Shift Register

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Serial In − Parallel Out SISO Shift Register

The shift register, which allows parallel input and produces serial output is known as

Parallel In − Serial Out PISO shift register. The block diagram of 3-bit PISO shift

register is shown in the following figure .

Parallel In − Serial Out SISO Shift Register

This circuit consists of three D flip-flops, which are cascaded. That means, output of one D flip-

flop is connected as the input of next D flip-flop. All these flip-flops are synchronous with each

other since, the same clock signal is applied to each one.

In this shift register, we can apply the parallel inputs to each D flip-flop by making Preset

Enable to 1. For every positive edge triggering of clock signal, the data shifts from one stage to

the next. So, we will get the serial output from the right most D flip-flop

Parallel In - Parallel Out PIPO Shift Register

The shift register, which allows parallel input and produces parallel output is known as Parallel In −

Parallel Out PIPO shift register. The block diagram of 3-bit PIPO shift register is shown in the

following figure.

This circuit consists of three D flip-flops, which are cascaded. That means, output of one D flip-flop

is connected as the input of next D flip-flop. All these flip-flops are synchronous with each other

since, the same clock signal is applied to each one.

In this shift register, we can apply the parallel inputs to each D flip-flop by making Preset Enable to

1. We can apply the parallel inputs through preset or clear. These two are asynchronous inputs. That

means, the flip-flops produce the corresponding outputs, based on the values of asynchronous inputs.

In this case, the effect of outputs is independent of clock transition. So, we will get the parallel

outputs from each D flip-flop.

•Shift register is used as Parallel to serial converter, which

converts the parallel data into serial data. I

•t is utilized at the transmitter section after Analog to Digital

Converter ADCADC block.

•Shift register is used as Serial to parallel converter, which

converts the serial data into parallel data.

•It is utilized at the receiver section before Digital to Analog

Converter DACDAC block.

•Shift register along with some additional gates generate the

sequence of zeros and ones.•Hence, it is used as sequence generator.

•Shift registers are also used as counters.

•There are two types of counters based on the type of output from

right most D flip-flop is connected to the serial input.

• Those are Ring counter and Johnson Ring counter.

COUNTERS

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A Counter is register, which is capable of counting the number of clock pulse, which have arrived at

its clock input. These counters are used for counting pulses in large variety of counting applications

such as control systems,computers,electronic and scientific instruments, etc.

Conters can be classified into following two types.

Asynchronous counters or ripple counter

Synchronous counters

A ripple counter is also called an asynchronous counter, because it is an asynchronous

sequential circuit.

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UNIT-III

Input-Output Interface

i)I /O Bus and interface Modules

-The I/O bus consists of data lines, address lines andcontrol lines.-The magnetic disk, printer and terminal are employed inany general purpose computers.-The magnetic tape is used in some computers for backup storage.-Each interface decodes the address and control received from the I/O bus, intercepts them for the peripheral, and provides signal for the peripheral controller.

-Each peripheral has its own controller that operates the particular electromechanical device.

-The I/O bus from the processor is attached to all peripheral interfaces.

Control command- is used t activated the peripheral and to inform it what to do.

Status command- is used to test various status conditions in theinterface and the peripheral.

Data Output command-causes the interface to respond by transferring data from the bus into one of its register.

Input Data command- is the opposite of the data output.

ii)I/O Bus versus Memory bus

ii)Isolated versus Memory-Mapped I/O

Asynchronous Data Transfer

i)Strobe controlii) Handshaking

Priority Interrupt: Daisy- Chaining Priority

Parallel Priority InterruptDirect Memory Access:

DMA ControllerDMA Transfer

Input – Output Processor:CPU-IOP Communication

Priority interrupt

Two methods1.Software priority interrupts

-Polling2.Hardware Priority Interrupt-Serial Priority (Daisy Chaining)

-Parallel Priority

• A Priority interrupt is a system that Establishes apriority over various sources to determine whichcondition is to be serviced first when two or morerequest arrive simultaneously.

• The system may also determine which conditionare permitted to interrupt the computer whileanother interrupt is being serviced.

• When two devices interrupt the computer at thesame time, the computer services the device, withthe higher priority first.

Priority Interrupt

• Devices with high-speed transfers such as magnetic disks are given

higher priority, and slow devices such as keyboard or mouse receive

low priority.

Software Priority interrupt: Polling operation

Polling is the software method of establishing priority of

simultaneous interrupt.

In this method when a processor detects an interrupt ,it branches

interrupt service routine.

The order in which they are tested determines the priority of each

interrupt.

The highest priority source is tested first, and if its interrupt signal is on,

control branches to a service routine for this source.

Disadvantage of polling:

If there are many interrupt sources the time required to poll them can be

exceed the time available to service the I/O device

It is very time consuming. 1 2 3 4 5 6 7 8 .

Hardware Priority Interrupt

It accepts interrupt requests from many sources,determines which of the incoming requests hasthe highest priority, and issues an interruptrequest to the computer based on thisdetermination.To speed up the operation ,each interrupt sourcehas its own interrupt vector to access its ownservice routine directly.The hardware priority function can be establishedby either serial or parallel connection of interruptlines.

It consist of serial connection of all devicesthat request an interrupt.The devices with highest priority is placed inthe first position, followed by lower prioritydevices up to the device with the lowestpriority which is placed last in the chain.

• The CPU responds to an interrupt request by enablingthe interrupt acknowledge line.

• If any device has its interrupt signal in the low levelstate, the interrupt line goes to the low level state andenabled the interrupt input in the CPU.

• The signal is received by device 1 at its P1(priorityin)input.

• The acknowledge signal passes on to the next device tothrough the PO(priority out)output only if device 1 isnot requesting an interrupt.

• If device 1 has pending interrupt, it blocks theacknowledge signal from the next device by placing a0 in the PO output.

• It then proceeds it to insert its own interrupt vectoraddress into the data bus for the CPU to use during theinterrupt cycle.

UNIT IVMemory Organization: -Memory Hierarchy – Main MemoryAssociative memory: -Hardware Organization-Match Logic-Read Operation-Write OperationCache Memory:

-Associative-Direct-Set-associative Mapping-Writing into Cache

-Cache InitializationVirtual Memory:-Address Space and Memory Space-Address Mapping Using Pages-Associative Memory Page Table-Page Replacement

MEMORY HIERARCHY IN A COMPUTER SYSTEM

Magnetictapes

Magneticdisks

I/Oprocessor

CPU

Mainmemory

Cachememory

Auxiliary memory

Register

Cache

Main Memory

Magnetic Disk

Magnetic Tape

Memory Hierarchy is to obtain the highest possibleaccess speed while minimizing the total cost of the memory system

Memory Hierarchy

MAIN MEMORY

RAM and ROM Chips

Typical RAM chip

Typical ROM chip

Chip select 1

Chip select 2

Read

Write

7-bit address

CS1

CS2

RD

WR

AD 7

128 x 8RAM

8-bit data bus

CS1 CS2 RD WR

0 0 x x0 1 x x1 0 0 01 0 0 11 0 1 x1 1 x x

Memory function

InhibitInhibitInhibitWriteReadInhibit

State of data bus

High-impedenceHigh-impedenceHigh-impedenceInput data to RAMOutput data from RAMHigh-impedence

Chip select 1

Chip select 2

9-bit address

CS1

CS2

AD 9

512 x 8ROM

8-bit data bus

Main Memory

Associative memory-Hardware Organization

-Match Logic-Read Operation-Write Operation

Output

Memory

Cache Memory-Associative

-Direct-Set-associative Mapping

-Writing into Cache-Cache Initialization