Instruction fetch execution cycle

Current Instruction Register (CIR) - this holds the current instruction being executed. Memory Address Register (MAR) - this holds the RAM address you FETCH. The CPU reads the contents of the Program Counter to find the address of the next instruction to be fetched, decoded and executed. The execution of an instruction includes several memory operations and not all instructions execute the same number of memory operations. On the MSP430, this is done at the end of the same clock cycle as the instruction is fetched. Any input operands stored in memory must also be fetched. An Execution Cycle often requires more than one clock cycle to complete and has multiple steps to complete execution. Fetch Instruction: Fetch instruction from the instruction queue. Execution Cycle. Fetch An instruction, stored in the memory, is fetched into the control unit by supplying the memory with the address of the instruction. The memory accesses will be split into instruction fetches and data accesses (since data accesses are often slower). Fetch Cycle: The fetch cycle begins with retrieving the address stored in the Program Counter (PC). Execute Cycle: This cycle as the name suggests, simply executes the instruction that was fetched and decoded. Interrupt Cycle: An interrupt can occur any time during the program execution. Five instruction execution steps Instruction fetch Instruction decode and register read Execution, memory address calculation, or branch completion Memory access or R-type instruction completion Write-back Instruction execution takes 3~5 cycles! Instruction fetch cycle: Get instructions from memory and analyze instructions. Indirect address cycle: Indirect addressing instructions Execution cycle: Except for no-ops and NOP instructions, all instructions include an execution cycle to complete the main functions of the instruction. 18.1 Instruction Execution The Von Newman architecture model of a computer states that the CPU is responsible for reading instructions from the memory system and executing them. The CPU operates by following the so called fletch-decode-execute cycle: Fetch the operation word. An instruction cycle (sometimes called fetch-and-execute cycle, fetch-decode-execute cycle, or FDX) is the basic operation cycle of a computer. It is the process by which a computer retrieves a program instruction from its memory, determines what actions the instruction requires, and carries Machine cycle and Instruction cycle. SAP1 has six T-states (three fetch and three execute cycles) reserved for each instruction. Not all instructions require all the six T-states for execution. The unused T- state is marked as No Operation (NOP) cycle. Each T-state is called a machine cycle for n IF - Instruction Fetch n ID - Instruction Decode n EX - Instruction Execution n MEM - Memory Access n WB - Register Write Back. n Two techniques: n Superscalar a A superscalar processor executes more than one instruction during a clock cycle. n VLIW a very long instruction word The process of cycling instructions may also be known as the E-cycle (execution cycle), I-cycle (instruction cycle), fetch-decode-execute cycle, or fetch-execute cycle. Execute - Execute the computer commands. Store - Send and write the results back in memory. Example of a machine cycle. The process of cycling instructions may also be known as the E-cycle (execution cycle), I-cycle (instruction cycle), fetch-decode-execute cycle, or fetch-execute cycle. Execute - Execute the computer commands. Store - Send and write the results back in memory. Example of a machine cycle. Fetch Cycle: Processor reads (fetches) instruction from memory one at a time is called "fetch cycle". Program execution consists of repeating the process of instruction fetch and execution. Program execution halts only if the machine is turned off.