Fetch execute cycle
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Fetch-Execute cycle PowerPoint PPT Presentation


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Fetch-Execute cycle. Memory Read operation. Read from memory. PC. Main Memory. 1. MAR. Address bus. Other registers. Data bus. MDR. Control bus. ALU. Control Unit. Clock pulses. The Program Counter (PC) holds the address of the next instruction. Electronic Clock. PC. Main

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Fetch-Execute cycle

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Fetch execute cycle

Fetch-Execute cycle


Memory read operation

Memory Read operation

Read from memory


Fetch execute cycle

PC

Main

Memory

1

MAR

Address bus

Other

registers

Data bus

MDR

Control bus

ALU

Control

Unit

Clock pulses

The Program Counter (PC) holds the address of the next instruction

Electronic

Clock


Fetch execute cycle

PC

Main

Memory

10110111

1

MAR

Address bus

Other

registers

Data bus

MDR

Control bus

ALU

Control

Unit

Clock pulses

The contents of the PC are copied to the Memory Address Register (MAR)

Electronic

Clock


Fetch execute cycle

PC

Main

Memory

1

MAR

Address bus

Other

registers

10110111

Data bus

MDR

Control bus

ALU

Control

Unit

Clock pulses

Memory address to be accessed is placed onto the address bus

Electronic

Clock


Fetch execute cycle

PC

Main

Memory

1

MAR

Address bus

Other

registers

Data bus

MDR

Control bus

ALU

Control

Unit

>>read>>

Clock pulses

Electronic

Clock

The control bus sends a read signal


Fetch execute cycle

PC

Main

Memory

01010111

1

MAR

Address bus

Other

registers

Data bus

MDR

Control bus

ALU

Control

Unit

The contents of the memory location are passed along the data bus to the Memory Data Register (MDR)

Clock pulses

Electronic

Clock


Fetch execute cycle

PC

Main

Memory

2

1

MAR

Address bus

Other

registers

Data bus

MDR

Control bus

ALU

Control

Unit

Clock pulses

The PC is incremented ready for the next instruction

Electronic

Clock


Memory write operation

Memory Write operation

Write to memory


Fetch execute cycle

PC

Main

Memory

2

MAR

Address bus

Other

registers

Data bus

MDR

1110011

Control bus

ALU

Control

Unit

Clock pulses

Electronic

Clock

Data is placed onto the data bus


Fetch execute cycle

PC

Main

Memory

2

MAR

Address bus

Other

registers

11110010

Data bus

MDR

Control bus

ALU

Control

Unit

Clock pulses

Memory address to be written to is placed onto the address bus

Electronic

Clock


Fetch execute cycle

PC

Main

Memory

2

MAR

Address bus

Other

registers

Data bus

MDR

Control bus

ALU

Control

Unit

>>write>>

Clock pulses

Electronic

Clock

A ‘write’ signal is sent along the control bus


Fetch execute cycle

PC

Main

Memory

2

MAR

Address bus

Other

registers

Data bus

MDR

10111110

Control bus

ALU

Control

Unit

Clock pulses

Electronic

Clock

The data is transferred to the destination in memory


Fetch execute cycle

PC

Main

Memory

3

2

MAR

Address bus

Other

registers

Data bus

MDR

Control bus

ALU

Control

Unit

Clock pulses

Electronic

Clock

The PC is incremented


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