Practice question · Select all that apply
The CPU is executing ADD R1, R2, writing the result back into R1. Select every control signal the control unit must produce for this instruction.
Hints
- Trace the operands' route: out of some registers, through the ALU, back to somewhere.
- Two of the options describe work that belongs to a different instruction family entirely.
Show the answer
- B. Whether the ALU should add or subtract
- C. Which register the ALU's result is written back to
- E. Which registers to read onto the ALU's inputs
Why
An arithmetic instruction needs its sources selected, the ALU's function chosen, and its destination selected, three signals along one route. It touches no memory address (that would be a data-transfer instruction) and sets no PC target (that would be control flow). Assuming every instruction touches memory is the trap.
Practise Data Path and Control
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