8085 Instruction Cycle Explained

The complete sequence of operations performed by the 8085 microprocessor to fetch an instruction from memory, decode it, and then execute it is known as the Instruction Cycle.

The Instruction Cycle is the fundamental process that a CPU follows to execute a program instruction. It typically consists of two main stages:

• Fetch Stage: The processor retrieves the instruction from the memory location pointed to by the program counter (PC).
• Execute Stage: The processor decodes the fetched instruction and performs the required operations (e.g., arithmetic, logic, data transfer, control flow).

While other terms relate to processor operations, they don't represent the entire fetch-and-execute sequence:

• Machine Cycle: A machine cycle is a subdivision of the instruction cycle, representing a basic step like fetching data from memory or performing an I/O operation. An instruction cycle can comprise one or more machine cycles.
• Memory Cycle: This term refers specifically to the operations involving memory access (reading or writing), which is only a part of the fetch or execute stages.
• Clock Cycle: This is the basic time unit or period of the system clock. Multiple clock cycles constitute a machine cycle, and multiple machine cycles form an instruction cycle.

Therefore, the Instruction Cycle accurately describes the entire process required to fetch and execute an instruction.