computer orgnization rabie a. ramadan lecture 6. datapath
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Computer Orgnization
Rabie A. Ramadan
Lecture 6
DataPath
Execute Simple Arithmetic Operation
Show the steps executing the following instruction on One-Bus , Two-Bus, and Three-Bus Organizations:
Add R1, R2, R0
(Add R1 to R2 and save the results in R0)
One-Bus Organization
Add R1, R2, R0
Answer
Two-Bus Organization
Add R1, R2, R0
Answer
Two-Bus Organization
Add R1, R2, R0
Answer
Three-Bus Organization
Add R1, R2, R0
Answer
CPU INSTRUCTION CYCLE
Get the instruction from the memory Increment the PC Decode the Instruction Execute it during execution is there any interrupt (ex. Keyboard input)? Handling the interrupt or continue executing the instruction is left to the code designer
Interrupt Handling
Interrupt• An asynchronous signal from hardware indicating the need for
attention.
• A synchronous event in software indicating the need for a change in execution
Ex. • Input from the Keyboard
• Incoming message from the network card
How the control unit can manage to execute such instructions?
Control Unit
Control Unit Controls the flow of data
• CPU and external units (memory, I/O)
Control Bus
• Carry the signal between the control unit and other components.
Decoder
• Decode the instruction (Op-code)
Control Unit Clock Signal
• Used to synchronize instructions execution
Control Signal Generator • Controlled by :
• Decoder signal
• Enabled time signal
• Other inputs (eg. Interrupt signal)
Put All Together
Example
Using one-Bus organization, show the control sequence needed to execute the following instruction:
Add R1, R2, R0
Answer
Answer (Cont.) Control Unit Signals
Types of Control Units Microprogrammed
• Flexible
• Can be reprogrammed with new instructions using microprogram • Microprogram
• Program stored in memory that generates all the control signals required to execute the instruction set correctly
Wired• Inflexible
• Once the control unit of a hard-wired computer is designed and built, it is virtually impossible to alter its architecture and instruction set.
Hardwired Control Unit
Needs logic circuit designer
Input A Input B Output Q
0 0 0
0 1 1
1 0 1
1 1 1
Input A Input B Output Q
0 0 1
0 1 1
1 0 1
1 1 0
Example Design a control unit that has 3 instruction sets
inst-x, inst-y, inst-z and A,B,C,D,E,F and G control lines The lines that have to be activitied based on the time signals are :
(e.g. if t0 =1 and inst-x =1 lines D,B, E must equal 1 )
A,B,…..,F
The Design
A= inst-x.t1 + inst-z.t1 = t1.(inst-x+inst-z)
B = inst-x.t0 + inst-y.t2
C = inst-x . t1 + inst-x. t2 + inst-y.t2 + inst-z. t1 = t1. (inst-x + inst-z) + (inst-x + inst-y). t2 = A + (inst-x + inst-y). t2 E =...
The Final Design
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