51单片机基础篇 对于有一定基础的人看看 包含书中所以的源代码

				     ;FUNCTION NAME: CLEAR_EXTERNAL_MEMORY
				     ;FUNCTION: CLEAR 2KB EXTERNAL DATA MEMORY
				     ;EXTERNAL DATA MEMORY ADDRESS IN DPTR
				     ;
				     CLEAR_EXTERNAL_MEMORY
				           	CLR  	A
				           	MOV  	R2,#08H
				     $1 	MOV  	R1,#00H
				     $2 	MOVX  	@DPTR,A
				           	INC   	DPTR
				           	DJNZ 	R1,$2
				           	DJNZ 	R2,$1
				           	RET
				     ;