Procedure II: Subtraction with and without borrow

$1$

A$.$ Lets subtract $33H({51}_{10})$ from $A5H({165}_{10}).$ We should get $72H({114}_{10}).$ FIRST write all the following code, which uses SUB to perform subractions that do not require a borrow, THEN single step, recording data as required:

MOV AL$,$A$5$

MOV BL$,33$

SUB AL$,$BL

AL:

BL:

MOV AX$,2771$

MOV CX$,00$B$3$

MOV BX$,87$A$0$

MOV DX$,0004$

SUB AX$,$BX

AX:

Carry Flag:

Carry Flag:

; CX$,$AX loaded with B$32771$H

; DX$,$BX loaded with $487$A$0$H

; subtract the lower $16-$bits

Question $5$: Is the carry bit set? Why? B$32771$ is larger than $487AO.$

SBB CX$,$DX

; now we subtract the upper $16$ bits with borrow

$Ax$

$Cx$: