Characteristics and Classification of Machine Cycle

Characteristics and Classification of Machine Cycle

Hi!

Yes. Machine cycle, also known as "processor cycle" and "instruction cycle", is the completion of the series of 4 steps (basic operation) that a CPU executes for each machine language instruction. This is carried out continuously with a rate of millions per second by the CPU (Central Processing Unit). 

These 4 steps are:

1. Fetch 2. Decode 3. Execute 4. Store.

• Step 1 (Fetch) refers to the reading of the machine language instruction.
• Step 2 (Decode) refers to interpreting the read machine language instruction into a code.
• Step 3 (Execute) refers to the execution of the code.
• Step 4 (Store) refers to the storing of the code in the memory.
• Machine cycles are classified as "Status signals" and "Control signals".
• For an 8085 microprocessor, the available types of machine cycle are Opcode fetching, Memory Read, Memory writes, I/O Read, I/O Write, INTR Acknowledge, and Bus Idle.

Hope this helps you.

Characteristics and Classification of Machine Cycle

The other term for “machine cycle” is “processor cycle” or “instruction cycle”. This is the basic operation performed by a CPU or Central Processing Unit. Machine cycle is composed of a series of three steps performed continuously at a rate of millions per second while a computer is in operation. These three steps are fetch, decode, and execute.

There is also a fourth step called “store” wherein input and output from the other three phases is stored in the memory for later use but there is no actual processing performed in this step. In the fetch step, the control unit requests instructions from the main memory stored at a memory’s location indicated by the program counter or the instruction counter.

In the decode step, received instructions are decoded in the instruction register which includes breaking the operand field down to its components based on the instruction’s opcode or operation code. In the execute step, this includes the instruction’s opcode because it specifies the required CPU operation. The program counter indicates the instruction sequence for the computer.

These instructions are arranged into the instructions register and as every instruction is executed, the program counter is incremented so that the next instruction is stored in the memory. The right circuitry is then activated to perform the requested task. As soon as the instructions have been executed, it restarts the machine cycle which begins the fetch step.