fetch decode and execute cycle

Explian the fetch decode and execute cycle?

A standard process which describes the steps needed  for the processing. This cycle is called the fetch decode and execute cyle which have three parts which include fetching the data then decode it and at last execute that data .First of all both data and the program that acts upon that data are loaded into main memory(RAM) by the operating system.The CPU is now ready to work.

First Step;

1;Fetch the instruction .To start the cycle,The BIU places a memory read request on the control bus and the address of the instruction on the address bus.Memory responds by sending  the contents of the location specified -namely  the instruction code just given-over  the data bus, because the instruction code is of four byte and the 8086 can only read a word at a time this involves  two read operation .The CPU assepts the data and adds  four  to the IP will contain the address of the next instruction.

Second  Step;

2; The next  step  is for the CPU to make sense of the instruction it has just  fetched. This is called decode. On receiving  the  instruction,a decoder circuit in the EU decodes the instruction and determine that it is an ADD operation involving the word at address 0. The CPU is designed to understand a specific set of commands.

Third Step;

3;This is the part of cycle when data processing actually take place. This instruction is carried out upon the data. This result of processing is stored in yet another register. Once the execute stage is complete.The Cpu sets  itself up to begin another cycle once more.