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At the beginning of each instruction cycle, the processor fetches an instruction from memory. In a typical processor, a register called the program counter (PC) holds the address of the instruction to be fetched next. Unless told otherwise, the processor always increments the PC after each instruction fetch so that it will fetch the next instruction in sequence. The fetched instruction is loaded into a register in the processor known as the instruction register (IR). The instruction contains bits that specify the action the processor is to take. The processor interprets the instruction and performs the re­quired action.

Execute cycle:

In general, the required actions fall into four categories:

  • Processor-memory: Data may be transferred from processor to memory or from memory to processor.
  • Processor-I/O: Data may be transferred to or from a peripheral device by transferring between the processor and an I/O module.
  • Data processing: The processor may perform some arithmetic or logic opera­tion on data.
  • Control: An instruction may specify that the sequence of execution be altered.
  • An instruction’s execution may involve a combination of these actions.

Instruction cycle state diagram:

Figure 4 provides a more detailed look at the basic instruction cycle. The figure is in the form of a state diagram. For any given instruction cycle, some stales may be null and others may be visited more than once. The states can be described as follows:

Figure 4: Instruction cycle state diagram

  • Instruction address calculation (iac): Determine the address of the next instruction to be executed. Usually, this involves adding a fixed number to the address of the previous instruction. For example, if each instruction is 16 bits long and memory is organized into 16-bit words, then add 1 to the previous address. If, instead, memory is organized as individually addressable 8-bit bytes, then add 2 to the previous address.
  • Instruction fetch (if): Read instruction from its memory location into the processor.
  • Instruction operation decoding (iod): Analyze instruction to determine type of operation to he performed and operand(s) to be used.
  • Operand address calculation (oac): If the operation involves reference to an operand in memory or available via I/O. then determine the address of the operand.
  • Operand fetch (of): Fetch the operand from memory or read it in from I/O,
  • Data operation (do): Perform the operation indicated in the instruction.
  • Operand store (os): Write the result into memory or out to I/O

2.2 interrupts

Virtually all computers provide a mechanism called Interrupt, by which other modules (I/O. mem­ory) may interrupt the normal processing of the processor. Interrupts are provided primarily as a way to improve processing efficiency.

For example, most external devices are much slower than the processor. Suppose that the processor is transferring data to a printer using the instruction cycle scheme of Figure 3. After each write operation, the processor must pause and remain idle until the printer catches up. The length of this pause may be on the order of many hundreds or even thousands of instruction cycles that do not involve memory. Clearly, this is a very wasteful use of the processor. The figure 5a illustrates this state of affairs.

Questions & Answers

A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
Aislinn Reply
cm
tijani
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John Reply
what is physics
Siyaka Reply
A mouse of mass 200 g falls 100 m down a vertical mine shaft and lands at the bottom with a speed of 8.0 m/s. During its fall, how much work is done on the mouse by air resistance
Jude Reply
Can you compute that for me. Ty
Jude
what is the dimension formula of energy?
David Reply
what is viscosity?
David
what is inorganic
emma Reply
what is chemistry
Youesf Reply
what is inorganic
emma
Chemistry is a branch of science that deals with the study of matter,it composition,it structure and the changes it undergoes
Adjei
please, I'm a physics student and I need help in physics
Adjanou
chemistry could also be understood like the sexual attraction/repulsion of the male and female elements. the reaction varies depending on the energy differences of each given gender. + masculine -female.
Pedro
A ball is thrown straight up.it passes a 2.0m high window 7.50 m off the ground on it path up and takes 1.30 s to go past the window.what was the ball initial velocity
Krampah Reply
2. A sled plus passenger with total mass 50 kg is pulled 20 m across the snow (0.20) at constant velocity by a force directed 25° above the horizontal. Calculate (a) the work of the applied force, (b) the work of friction, and (c) the total work.
Sahid Reply
you have been hired as an espert witness in a court case involving an automobile accident. the accident involved car A of mass 1500kg which crashed into stationary car B of mass 1100kg. the driver of car A applied his brakes 15 m before he skidded and crashed into car B. after the collision, car A s
Samuel Reply
can someone explain to me, an ignorant high school student, why the trend of the graph doesn't follow the fact that the higher frequency a sound wave is, the more power it is, hence, making me think the phons output would follow this general trend?
Joseph Reply
Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
Joseph
Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
Joseph
"Generation of electrical energy from sound energy | IEEE Conference Publication | IEEE Xplore" ***ieeexplore.ieee.org/document/7150687?reload=true
Ryan
what's motion
Maurice Reply
what are the types of wave
Maurice
answer
Magreth
progressive wave
Magreth
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Muhammad Reply
fine, how about you?
Mohammed
hi
Mujahid
A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?
yasuo Reply
Who can show me the full solution in this problem?
Reofrir Reply
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Source:  OpenStax, Computer architecture. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10761/1.1
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