Fetch-Decode-Execute cycle in Processor

 

Microprocessors used in Embedded applications follow the FETCH-DECODE-EXECUTE cycle. This is also called FETCH-EXECUTE cycle. The cycle speed depends entirely on the clock used.

In processors, we have something called Main memory or the primary memory which stores the instructions and the data. Main memory could be volatile as well as non-volatile. The non-volatile memory is RAM which has a copy of the entire program which need to be executed. Processor over a system bus communicates with the RAM to fetch the required instructions for next steps.

Once the instructions are fetched, the processor decodes the instructions. It is the instruction set which is followed by the processor that helps the processor to understand the instructions fetched and decoding them. If we take an ARM processor there are around 2^32 instructions. the instruction set is different for different processors.

RISC based processors which place emphasis on using registers is from where the operands are fetched for execution. Once the execution is completed and result is saved to a register the processor moves to the next fetch cycle.