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The instruction cycle (also known as the fetch–decode–execute cycle, or simply the fetch–execute cycle) is the cycle that the central processing unit (CPU) follows from boot-up until the computer has shut down in order to process instructions. It is composed of three main stages: the fetch stage, the decode stage, and the execute stage.
For example, to perform digital filters fast enough, the MAC instruction in a typical digital signal processor (DSP) must use a kind of Harvard architecture that can fetch an instruction and two data words simultaneously, and it requires a single-cycle multiply–accumulate multiplier.
A high-level illustration showing the decomposition of machine instructions into micro-operations, performed during typical fetch-decode-execute cycles [1]: 11 . In computer central processing units, micro-operations (also known as micro-ops or μops, historically also as micro-actions [2]) are detailed low-level instructions used in some designs to implement complex machine instructions ...
Opcode Instruction Mnemonic Machine Cycles 00: It is idle, doing fetch cycles (I think) IDL: 2 0N: Load D from address in RN: LDN N: 2 1N: Increment the 16 bit number in RN: INC N: 2 2N: Decrement the 16 bit number in RN: DEC N: 2 30 MM: Branch R(P) unconditionally to MM: BR: 2 31 MM: Branch R(P) to MM if Q is 1: BQ: 2 32 MM: Branch R(P) to MM ...
New opcodes that introduced new functionality (e.g. SHLD, SETcc) For instruction forms where the operand size can be inferred from the instruction's arguments (e.g. ADD EAX,EBX can be inferred to have a 32-bit OperandSize due to its use of EAX as an argument), new instruction mnemonics are not needed and not provided.
The binary opcodes (machine language) were identical, but preceded by a new opcode prefix. [52] Zilog published the opcodes and related mnemonics for the intended functions, but did not document the fact that every opcode that allowed manipulation of the H and L registers was equally valid for the 8 bit portions of the IX and IY registers.
In computer engineering, instruction pipelining is a technique for implementing instruction-level parallelism within a single processor. Pipelining attempts to keep every part of the processor busy with some instruction by dividing incoming instructions into a series of sequential steps (the eponymous "pipeline") performed by different processor units with different parts of instructions ...
Both CPUs evaluate branches in the decode stage and have a single cycle instruction fetch. As a result, the branch target recurrence is two cycles long, and the machine always fetches the instruction immediately after any taken branch. Both architectures define branch delay slots in order to utilize these fetched instructions.