SETB P3.0
ACALL SCANKEYPAD
ACALL DEBOUNCE
DEBOUNCE:MOV R3,#0H
         ACALL SUBDEBOUNCE

SUBDEBOUNCE:INC R3
	    ACALL SCANKEYPAD
	    ACALL CHECK

SCANKEYPAD:MOV R0,#07FH
           MOV R4,#0H
	   CLR P3.0           
SCAN:CLR P3.0
     MOV A,R0
     RL A
     MOV R2,P1
     MOV R5,P1
     MOV R0,A
     ANL A,R2
     INC R4
     CJNE R4,#4H,SCAN1
     ACALL iff1
     iff1:CJNE R3,#0H,iff
     iff:JNB P3.0,DEBOUNCE
     ACALL SCANKEYPAD
SCAN1:MOV B,R5
      CJNE A,B,SCAN
      SETB P3.0

CHECK:	    JNB P3.0,DEBOUNCE
	    CJNE R3,#64H,SUBDEBOUNCE
	    JB P3.0,KEYPRESSED
	    ACALL NOKEYPRESSED

KEYPRESSED:MOV P2,R5 ;P2 will show that which key has been pressed.
NOKEYPRESSED:NOP        
END