
41
CHAPTER 2 BASICS OF SOFTWARE
DSUBS
Makes subtrahend positive
Sign flag SFLAG
←
0
Makes subtrahend positive
Sign flag SFLAG
←
1
A
←
[DE] – [HL] – CY
Subtracts subtrahend from
minuend with CY
DE
←
DE + 1, HL
←
HL + 1
Increments subtrahend
and minuend addresses
B
←
C, CY
←
0
Minuend < 0
Adjusts result to decimal
and stores in memory
Yes
C = 0
Inverts sign flag that takes
10's complement
Yes
DSUBS1
Result = 0
No
Yes
No
Sign flag = 1
Yes
No
RET
DSUBS2
C
←
C – 1
CY = 1
Yes
Appends negative sign to result
DSUBS5
No
No