2 ms·
How does the ALU handle the fact that INC/DEC do not update the carry flag? Different control signals depending on the ALU operation being performed? Also, doe
by bonzini 4y ago
How does the ALU handle the fact that INC/DEC do not update the carry flag? Different control signals depending on the ALU operation being performed?
Also, does LOOP use a different ALU operation to decrement CX, since it doesn't update the flags at all?
- kens 4y agoThe INC/DEC instructions block the control signal that updates the carry flag. This happens in the carry flag circuit.(See footnote 10.) For LOOP, the microcode doesn't have the F bit set, so the flags aren't updated from the ALU. Same with NOT.