Question

Show the steps of the CPU fetch–execute cycle (micro operations)

for an instruction that produces the 2’s complement of the number
in accumulator A (calculator).

Answer 1

The fetch-execute cycle is a series of steps that the CPU follows to execute an instruction, in this case, to produce the 2's complement of a number in an accumulator. The cycle includes fetching, decoding, executing (inverting bits and adding 1), and storing the result.

Step-by-step explanation:

The fetch-execute cycle is when a computer's central processing unit (CPU) executes instructions. To perform a 2's complement on a number in the accumulator A, the following micro operations are involved:

1. 
   
3. Fetch: The CPU fetches the instruction from memory that tells it to perform the 2's complement operation.
4. 
   
6. Decode: The instruction is decoded to determine what actions must be taken.
7. 
   
9. Execute: The CPU performs the 2's complement operation:
10. 
    

• 
  
• Invert all the bits in the accumulator A.
• 
  
• Add 1 to the result of the inversion.
• 
  

Store: The resultant 2's complement number is stored back into the accumulator or another designated register.

This cycle repeats for each instruction executed by the CPU, ensuring that each operation is completed before moving on to the next instruction.