Stage 3: EXECUTE - "Do the Instruction"

Stage 3: EXECUTE - "Do the Instruction"

Purpose: Carry out the actual operation specified by the instruction

What Happens Depends on Instruction Type:

Arithmetic/Logic Operation (e.g., ADD, SUBTRACT, AND):

• The ALU performs the calculation or logic operation
• The result is stored in the Accumulator (ACC)
• Example: ADD 5 → ALU adds 5 to current ACC value → new total goes to ACC

Data Transfer (e.g., LOAD, STORE):

• LOAD: Data is copied from memory to a register (usually ACC)
• STORE: Data is copied from a register to memory
• Example: LOAD 200 → fetch data from memory address 200 → copy to ACC

Control Flow (e.g., JUMP, BRANCH, CALL):

• The PC is changed to a different address (not just +1)
• This allows loops, IF statements, and function calls
• Example: JUMP 100 → PC is set to 100 → next FETCH will get instruction from address 100

Different instructions take different amounts of time: A simple ADD might take 1 clock cycle, but a MULTIPLY might take several cycles.