SDADD:
MOV	R4,#00H					
MOV	R5,#40H					
MOV	R6,#60H					
MOV	R7,#01H					
MOV	20H,R4
MOV	21H,R5
ACALL	COMP					
MOV	R4,20H
MOV	R5,21H
MOV	20H,R6
MOV	21H,R7
ACALL	COMP					
CLR		C
MOV	A,R4
ADD		A,20H					
JB		D2,LOOP					
ACALL	COMP					
MOV	R4,20H					
MOV	R5,21H					
RET							
LOOP:
MOV	R4,#0FFH					
MOV	R5, #0FFH	
RET
COMP:
CLR		C						
MOV	A,20H
RLC		A
MOV	20H,A
MOV	A,21H
RLC		A						
MOV	21H,A
JNC		C,LOOP1
ACALL	NEGNVM
LOOP1:
MOV	A,21H
RRC	A						
MOV	20H,A
RET
NEGNVM:						
MOV	R0,20H
MOV	R1,21H
CLR		C						
CLR		A					
MOV	20H,A
MOV	21H,A
MOV	A,20H
SUBB	A,R0						
MOV	20H,A
MOV	A,21H
NOP
SUBB	A,R1					
MOV	21H,A
RET