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Central Processing Unit (Fetch Cycle). Central Processing Unit Programming Counter (PC) 1 The value stored in the program counter corresponds to the address.

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Presentation on theme: "Central Processing Unit (Fetch Cycle). Central Processing Unit Programming Counter (PC) 1 The value stored in the program counter corresponds to the address."— Presentation transcript:

1 Central Processing Unit (Fetch Cycle)

2 Central Processing Unit Programming Counter (PC) 1 The value stored in the program counter corresponds to the address of the instruction In memory which is next to be processed. 1Instruction Data FETCH

3 Central Processing Unit Program Counter (PC) 1 For the value to be used in the Program Counter, it is firstly transferred to the Memory Address Register (MAR) 1Instruction Data FETCH Memory Address Register (MAR) 1

4 Central Processing Unit Program Counter (PC) The program counter is now incremented by +1 so it points to the next instruction. 1Instruction Data FETCH Memory Address Register (MAR) 1 2

5 Central Processing Unit Program Counter (PC) The control unit checks the value in the memory address register before fetching the corresponding address in memory 1Instruction (I1) 2Instruction (I2) 3Instruction (I3) 4Instruction (I4) 5Data FETCH Memory Address Register (MAR) 1 2 Memory Data Register (MDA) Control Unit Memory Buffer Register (MBR)

6 Central Processing Unit Program Counter (PC) The fetched instruction is then stored in the MDR 1Instruction (I1) 2Instruction (I2) 3Instruction (I3) 4Instruction (I4) 5Data FETCH Memory Address Register (MAR) 1 2 Memory Data Register (MDA) I1 Control Unit Memory Buffer Register (MBR)

7 Central Processing Unit Program Counter (PC) The value in the Memory Data Register is transferred to the Current Instruction Register 1Instruction (I1) 2Instruction (I2) 3Instruction (I3) 4Instruction (I4) 5Data FETCH Memory Address Register (MAR) 1 2 Memory Data Register (MDA) I1 Control Unit Memory Buffer Register (MBR) Current Instruction Register (CIR) Instruction Register (IR) I1

8 Central Processing Unit Program Counter (PC) The instruction has been loaded into the CIR and is now ready to be decoded and executed. 1Instruction (I1) 2Instruction (I2) 3Instruction (I3) 4Instruction (I4) 5Data FETCH Memory Address Register (MAR) 1 2 Memory Data Register (MDA) Control Unit Memory Buffer Register (MBR) Current Instruction Register (CIR) Instruction Register (IR) I1

9 Central Processing Unit FETCH SUMMARY Program Counter Memory Address Register Program Counter+ 1 Control Unit Memory Address Register Instruction I1 Memory Data Register Current Instruction Register


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