ppt by mudit n vibhu

8/7/2019 ppt by mudit n vibhu

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Computer Operations1. Control Unit

2. Arithmetic and Logic Unit

3. Instruction Cycle


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Simple Computer


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Arithmetic

and

logic

unit

Control

unit

Memory

unit

Input/

output

unit

CPU

control bus

data bus

address bus

Simple Model Computer block diagramSimple Model Computer block diagram


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Arithmetic and logic unit

SR ACC

ALU

Arithmetic and Logical

operations are performed in

the ALU

1

ALU consists of an

accumulator (ACC), a set of

logic circuits, and a

status register (SR).

2


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Instruction

decoder PC

IR

Control unit

Control Unit

controls the overall

operations of the

computer.

1

Control Unit Consists

of the program

Counter (PC), the

instruction register (IR)

and the instructiondecoder.

2


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main memoryaddress decoder

MDR

MAR

Memory unit consists ofthe main store, the

memory data register

(MDR), the memory

address register (MAR),

and the address decoder.

1

Memory Unit 1

2Main store is composed of

a large number of memory

locations.


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Address decoder isresponsible for

selecting the

appropriate memory

location.

3

The memory data register holds

the piece of information read

from or written to the specified

memory location

4

The memory address registerholds the address of the

memory location to be

accessed.

5

Memory Unit 1


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Instruction Cycle


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Instruction Cycle

The instruction is fetched from memory

addressed by PC.

PC is advanced to address the next instruction.2

1

3 Instruction Decoder decodes theinstruction held in IR.

4 Instruction is then executed.

The process is repeated until the complete set

of instructions is fetched.


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Fetch instruction

from memory to IR

Increment PCExecute the

instruction

Decode the

instruction

Instruction Cycle


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main memory

SR

Instructiondecoder

addressdecoder

MDR

I/O unit

ACC

ALU

MAR

PC

IR


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main memory

SR

Instruction

decoder

address decoder

MDR

I/O unit

ACC

ALU

MAR

PC

IR

Memory unit


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main memory

SR

Instruction

decoder

address decoder

MDR

I/O unit

ACC

ALU

MAR

PC

IR

Memory unitControl unit


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Arithmetic and

logic unit main memory

SR

Instruction

decoder

address decoder

MDR

I/O unit

ACC

ALU

MAR

PC

IR

Memory unitControl unit


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Instruction

numberInstruction Address

location

1

2

3

10000

10001

10010Store the result held in the ACC

in memory location 11101

Load the contents in memorylocation 11111 into the ACC

Add the contents in memory

location 11110 to the ACC


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Main memory


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Load the contents in memory

location 11111 into the ACC


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Fetch cycle


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Fetch cycleFetch cycle- step 1

10000

PC


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PC

10000


MAR

10000

MAR


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10000

MAR

PC


Main memoryAddressdecoder

Instruction 1 10000

10000

Addressdecoder Main memory

10000


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10000

Main memoryFetch cycleFetch cycle

- step 4Addressdecoder

Instruction 1

Instruction 2

Instruction 3

10001

10010

11111

MDR

Instruction 1

Instruction 1 MDR

Number 1

10000

10000


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MDR

10000

10000


IRInstruction 1 IR Instruction 1Instruction 1


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Executing cycle


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Executing cycleExecuting cycle- step 1

1000010000PC

Instruction 1

PC10001

Instruction 1


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PCPC

Instruction 1Instruction 1


10000

Instruction

decoder

IR

10001

Instruction 1

10001

IR

Instruction

decoder


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Instruction

decoder

Instruction

decoder


10000

MAR

10001


11111

MAR


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Instruction 1

1111111111

MAR

Main memoryAddressdecoderAddressdecoder Main memory


Instruction 1

10001

11111

Number 1


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Instruction 1 MDR


Instruction 1

10001

11111

Number 1Number 1

MDRNumber 1

Number 1 11111

Main memory


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Instruction 1 MDRACC


10001

11111

Number 1

Number 1 Number 1ACC


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Fetch Executing


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Add the contents in memory

location 11110 to the ACC


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PC10001

MDRMDR

MAR

Number 1

PCPC


Instruction 2

10000

10001

10010

IR

Fetch cycleFetch cycle

Instruction 1

11111

Number 1

10001

Instruction 2


10001


10001

IR

10001

10001

Main memory

10001

MAR


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Executing cycleExecuting cycle

100011000111110

10001PCPC

10010

Number 1 Instruction 2Instruction 2Instruction 2

PC

Instruction

decoder

IR

10010

IR

Instruction

decoder

MAR

Instruction

decoder

MAR

11110


Number 2

Instruction 2

Number 2

MDRNumber 2

Number 2

ACCNumber 1Number 1Result

11110

MAR

11110

Main memory

ALU


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Store the result held in the ACC

in memory location 11101


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10010PC

MDRMDR

MAR


10000

IR

Fetch cycleFetch cycle

Instruction 1

11111

Number 1

10010

MARMAR


10010


10010

IR

10010

Main memory

10010


Result


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Main memoryMain memory

Result

100011000111101

10001PCPC

10011

Instruction 2Instruction 3Instruction 3

PC

Instruction

decoder

IR

10011

IR

Instruction

decoder

MAR

Instruction

decoder

MAR

11101

Addressdecoder

Number 2

Instruction 3

Result

MDRResultACCResult

11101

MAR

1110111101

Main memoryExecuting cycleExecuting cycle


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Summary

Register Abbreviation unction

Instruction

RegisterIR

Stores the current

instruction

Program

CounterPC

Stores the address of

the next instruction

to be executed.

InstructionDecoder

---

Decode the

instruction in IR

Control nit


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The End !!!

Thank You!!!

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