CPU Structure and Instruction Execution Timothy C. Rice Jr., MIT

Chapter Overview CPU Structure Flow of Data Execution Cycle - Fetch Cycle - Decode Cycle - Execute Cycle TCRJR

CPU Structure Simplified CPU Structure Diagram TCRJR

CPU Structure Arithmetic & Logical Unit (ALU) - deals with operations such as addition, subtraction, and multiplication of integers and Boolean operations - receives control signals from the control unit telling it to carry out these operations TCRJR

CPU Structure Control Unit (CU) - controls the movement of instructions in and out of the processor - controls the operation of the ALU - consists of a decoder, control logic circuits, and a clock to ensure everything happens at the correct time - responsible for performing the instruction execution cycle. TCRJR

CPU Structure Register Array - a small amount of internal memory - used for the quick storage and retrieval of data and instructions - Some registers are the program counter, instruction register, accumulator, memory address register and stack pointer. TCRJR

CPU Structure System Bus - comprised of the control bus, data bus and address bus - used for connections between the processor, memory and peripherals, and transferral of data between the various parts. TCRJR

CPU Structure Memory - not an actual part of the CPU - housed on the motherboard - where the program being executed is stored TCRJR

Flow of Data A flow diagram illustrating the flow of data within the PC during program execution and the saving of data. TCRJR

Instruction Execution Cycle Once a program is in memory it has to be executed. To do this, each instruction must be looked at, decoded and acted upon in turn until the program is completed. To ensure that the execution proceeds smoothly, it is also necessary to synchronise the activates of the processor. TCRJR

Instruction Execution Cycle TCRJR

Instruction Execution Cycle Fetch Cycle - Takes the address required from memory - Stores it in the instruction register - Moves the program counter on one so that it points to the next instruction. TCRJR

Instruction Execution Cycle Decode Cycle - Here, the control unit checks the instruction that is now stored within the instruction register. It determines which opcode and addressing mode have been used, and as such what actions need to be carried out in order to execute the instruction in question. TCRJR

Instruction Execution Cycle Instructions used in presentation TCRJR

Instruction Execution Cycle Execute - Here, the operation will take place. TCRJR

Summary The processor consists of 5 parts, the Arithmetic & Logic Unit, Control Unit, Register Array, System Bus, and the Memory. The instruction execution cycle has 3 processes namely the Fetch Cycle, Decode Cycle, and the Execute Cycle TCRJR

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