;按鍵掃描程序

SCAN:	MOV	A,#0FH
			MOV	P1,A
			MOV	A,P2
			ANL		A,#0FH
			CJNE		A,#0FH,NEXT1			;有鍵按下，則轉(zhuǎn)到NEXT1
			SJMP		NEXT4
;----------------------------------------
NEXT1:	CLR		P0.1
			SETB		P0.0
			ACALL	DS20MS				;延時(shí)20 ms，去抖動(dòng)
			CLR		C
			MOV	R2,#00H					;竄鍵標(biāo)志寄存器R2清0
			MOV	R1,#01H					;行掃描初值送R1
LOOP:	MOV	A,R1
			MOV		P1,A					;行掃描值送P1
			MOV	A,P2						;列值送A
			ANL		A,#0FH
			CJNE		A,#0FH,NEXT2			;若按鍵在本行，則NEXT2
			SJMP		NEXT3
;--------------------------------------------
NEXT2:	INC		R2
			CJNE		R2,#01H,NEXT4		;若竄鍵，則返回主程序
			MOV	R4,A
			MOV	A,R1
			MOV	R3,A
;---------------------------------------------
NEXT3:	MOV	A,R1						;行掃描值送A
			CLR		C
			RLC		A
			MOV	R1,A
			CJNE		A,#10H,LOOP
			AJMP		KCODE
;---------------------------------------------
NEXT4:	CLR		A
			AJMP		MAIN