The state diagram of an instruction cycle consist of five internal and three external states as shown below.

Above state diagram is for the instructions like :

1. ADD R,, R2

2. ADD R, , [R2]

3. ADD [R 1 ] , R2

To initiate execution of an inst the processor enters into lac (inst address calculation) Where the PC is prepared with proper memory addresses and then processor enter into state If (inst fetch). So that OP code of instruction is fetched from external memory and then processor enters into state Lod (inst oper" decode) where it understand which computation its ALU should perform more over. It also understand whether the data for predicated computation is in the processors reg's or it need to be fetched from mem. and if So then processor enters into state Oac (operated address calculi) where proper memory address is calculated and then processor enters into state of (operand fetch) to read data from memory. Thereafter processor enters into DO (data operation) state to carryout desired computation and then if that result of computation is required to be stored in memory then processor enters into state Oac and calculating proper address it enters into state Os (operand store) so that the result is stored is selected memory location and then processes resumes back to lac to calculate address of next inst of the program.