Here, First Instruction We will put the instruction address into the MAR register so we can fetch instruction from the memory.
This can be done by, PCr, MARw,MEMr
After Fetching the instruction from the memory, Instruction place in to the MBR register and from MBR to IR register it moves for execution.
This can be done by, MDRr, IRw
When instruction reaches to IR register, Decoder will start decoding of the instruction and it will find that first R1 register has to be fetched and put into the first temporary register.
This can be done by, R1r,Temp1w
After that, we have to fetch operand from the second register. After fetching both the operand ALU will start its work and stores result in the temporary register.
This can be done by, R2r,Temp1r,ALUadd,Temp2w
And at the last result stores into the destination register.
This can be done by, Temp2r,R0w.
So sequence is : 3,5,2,1,4