Intel 8080 - B4_Page_37

Chapter 6. Programming Techniques
Label Code
Operand Comment
DSUB:
LXI D,MINU
;D AND E ADDRESS MINUEND
LXI H,SBTRA ;H AND L ADDRESS SUBTRA-
;HEND
MVI C,8 ;EACH LOOP SUBTRACTS 2
;DIGITS (ONE BYTE),
;THEREFORE PROGRAM WILL
;SUBTRACT 16 DIGITS.
STC ;SET CARRY INDICATING
;NO BORROW
LOOP:
MVI
A,99H
;LOAD ACCUMULATOR
;WITH 99H.
ACI 0
;ADD ZERO WITH CARRY
SUB
M
;PRODUCE COMPLEMENT
;OF SUBTRAHEND
XCHG
;SWITCH
D AND E WITH
;H AND L
ADD
M ;ADD MINUEND
DAA ;DECIMAL ADJ UST
;ACCUMULATOR
MOV
M,A ;STORE RESULT
XCHG
;RESWITCH
D AND E
;WITH HAND L
DCR C
;DONE IF C
= 0
JZ
DONE
INX
D ;ADDRESS NEXT BYTE
;OF MINUEND
INX H
;ADDRESS
NEXT BYTE
;OF SUBTRAHEND
JMP
LOOP ;GET NEXT 2 DECIMAL DIGITS
DONE: NOP
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