2.2.3双字节有符号数减法.txt

本人保存经典的51程序

DSUB:         				
MOV    	A,R6
CPL    	ACC.7				
MOV    	R6,A
DADD:
MOV	A,R3
MOV	 C,ACC.7
MOV	SR0,C
XRL		A,R6
MOV	C,ACC.7
MOV	A,R3
CLR		ACC.7
MOV	R3,A
MOV	A,R6
CLR 		ACC.7
MOV	R6,A
JC		DAB2
NADD:								
MOV    	A,R4
ADD    	A,R7
MOV    	R4,A
MOV    	A,R3
ADDC   	A,R6
MOV    	R3,A
MOV    	A,R3
JB     	ACC.7,DABE
DAB1:
MOV 	C,SR0
MOV	ACC.7,C
MOV	R3,A
CLR		OV							
RET
DABE:
SETB   	OV
RET
DAB2:
LCALL 	 NSUB						
MOV	A,R3
JNB		ACC.7,DAB1
LCALL  	CMPT
CPL    	SR0
SJMP   	DAB1
RET