Fetch-Execute cycle. Memory Read operation Read from memory.
-
Upload
jesus-shackleton -
Category
Documents
-
view
221 -
download
0
Transcript of Fetch-Execute cycle. Memory Read operation Read from memory.
Fetch-Execute cycle
Memory Read operation
Read from memory
MainMemory
MAR
MDR
ControlUnit
ALU
Otherregisters
ElectronicClock
Clock pulses
Address bus
Data bus
Control bus
PC1
The Program Counter (PC) holds the address of the next instruction
MainMemory
MAR
MDR
ControlUnit
ALU
Otherregisters
ElectronicClock
Clock pulses
Address bus
Data bus
Control bus
PC1
The contents of the PC are copied to the Memory Address Register (MAR)
10110111
MainMemory
MAR
MDR
ControlUnit
ALU
Otherregisters
ElectronicClock
Clock pulses
Address bus
Data bus
Control bus
PC1
Memory address to be accessed is placed onto the address bus
10110111
MainMemory
MAR
MDR
ControlUnit
ALU
Otherregisters
ElectronicClock
Clock pulses
Address bus
Data bus
Control bus
PC1
The control bus sends a read signal
>>read>>
MainMemory
MAR
MDR
ControlUnit
ALU
Otherregisters
ElectronicClock
Clock pulses
Address bus
Data bus
Control bus
PC1
The contents of the memory location are passed along the data bus to the Memory Data Register (MDR)
01010111
MainMemory
MAR
MDR
ControlUnit
ALU
Otherregisters
ElectronicClock
Clock pulses
Address bus
Data bus
Control bus
PC1
The PC is incremented ready for the next instruction
2
Memory Write operation
Write to memory
MainMemory
MAR
MDR
ControlUnit
ALU
Otherregisters
ElectronicClock
Clock pulses
Address bus
Data bus
Control bus
PC2
Data is placed onto the data bus
1110011
MainMemory
MAR
MDR
ControlUnit
ALU
Otherregisters
ElectronicClock
Clock pulses
Address bus
Data bus
Control bus
PC2
Memory address to be written to is placed onto the address bus
11110010
MainMemory
MAR
MDR
ControlUnit
ALU
Otherregisters
ElectronicClock
Clock pulses
Address bus
Data bus
Control bus
PC2
A ‘write’ signal is sent along the control bus
>>write>>
MainMemory
MAR
MDR
ControlUnit
ALU
Otherregisters
ElectronicClock
Clock pulses
Address bus
Data bus
Control bus
PC2
The data is transferred to the destination in memory
10111110
MainMemory
MAR
MDR
ControlUnit
ALU
Otherregisters
ElectronicClock
Clock pulses
Address bus
Data bus
Control bus
PC2
The PC is incremented
3