BasicComputerOrganizationandDesign-2

BasicComputerOrganizationandDesign-2 - Kingdom Of Saudi...

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Basic Computer Organization and Design Chapter 5 in “Computer System Architecture” 1 Kingdom Of Saudi Arabia Al-Imam Muhammad Ibn Saud Islamic University College of Computer and Information Sciences Information System Department 1 st semester, 2010 – 2011 CS 224: Computer Organization T. Hala A. Al-Rumaih
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Instruction Cycle The program is executed in the computer by going through a cycle for each instruction. Each instruction cycle in turn is subdivided into a sequence of subcycles or phases. In the basic computer each instruction cycle consists of the following phases: Fetch an instruction from memory. Decode the instruction. Read the effective address from memory if the instruction has an indirect address. Execute the instruction. Upon the completion of step 4, the control goes back to step 1 to fetch, decode, and execute the next instruction 1. This process continues indefinitely unless a HALT instruction is encountered. 2
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Instruction Cycle (Cont.) Fetch and Decode: Initially, the program counter PC is loaded with the address of the first instruction in the program. The sequence counter SC is cleared to 0, providing a decoded timing signal T0. After each clock pulse, SC is incremented by one, so that the timing signals go through a sequence T 0 , T 1 T 2 , and so on. The microoperations for the fetch and decode phases can be specified by the following register transfer statements: T 0 : AR←PC T 1 : IR ← M[AR], PC ← PC + 1 T 2 : D0,. .., D7 ← Decode IR(12-14), AR ← IR(O-11), I< ← IR(15) 3
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Instruction Cycle (Cont.) The following figure shows how the first two register transfer statements are implemented in the bus system. 4
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Instruction Cycle (Cont.) Determine the Type of Instruction: The timing signal that is active after the decoding is T3. During time T3, the control unit determines the type of
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This note was uploaded on 02/09/2012 for the course CSCI 504 taught by Professor Jon during the Spring '11 term at IUP.

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BasicComputerOrganizationandDesign-2 - Kingdom Of Saudi...

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