书籍8051入门篇

				;8-5-3.ASM
				;2 BYTE DATA  SUBSTRACT
				$MOD51
					ORG	0000H
					MOV	R0,#20H
					MOV	R1,#30H
					CLR	CY
					MOV	A,@R0		;A=(20H)
					SUBB	A,@R1		;A=(20H)-(30H)		
					MOV	@R1,A		;(30H)=(20H)-(30H)
					INC	R0		;R0=21H
					INC	R1		;R1=31H
					MOV	A,@R0		;A=(21H)
					SUBB	A,@R1		;A=(21H)-(31H)-CY
					MOV	@R1,A		;(31H)=(21H)-(31H)-CY
					END