Intel 8080 - B4_Page_36

Chapter 6. Programming Techniques
6-16
5. Add the minuend digits 58 to the accumulator.
Accumulator = 001110008
58 = 010110008
~ 100100008 = 90H
Carry = 0 ~ 'AuXiliary Carry = 1
6. DAA
converts accumulator to 96 (since Auxiliary Carry = 1) and leaves carry flag = 0
indicating that a borrow occurred.
7. Load accumulator with 99H.
8. Add zero with carry to accumulator, leaving accumulator = 99H.
9. Subtract the subtrahend digits 13 from the accumulator.
Accumulator = 100110018
13=111011018
lJl 000011 08
10. Add the minuend digits 43 to the accumulator.
Accumulator = 100001108
43 = 010000118
~~ 110010018 = C9H
Carry
= 0 'AuXiliary Carry = 0
11. DAA converts accumulator to 29 and sets the carry flag'" 1, indicating no borrow occurred.
Therefore, the result of subtracting 1362 from 4358 is 2996.
The following subroutine will subtract one 16-digit decimal number from another using the following assumptions:
The minuend is stored least significant (2) digits first beginning at location MINU.
The subtrahend is stored least significant (2) digits first beginning at location S8TRA.
The result will be stored least significant (2) digits first, replacing the minuend.