DELAY_HIGH EQU 003H
		DELAY_LOW EQU 018H
	
		FLAG_0 EQU 031H
		FLAG_1 EQU 032H
		FLAG_2 EQU 033H
		FLAG_3 EQU 034H
		FLAG_4 EQU 035H
		FLAG_5 EQU 036H
		FLAG_6 EQU 037H
		FLAG_7 EQU 038H
		FLAG_INVALIDKEY EQU 039H
		FLAG_PUSH EQU 040H
		NEWKEY EQU 041H

                            ORG 000H
			MOV SP,#050H
			LJMP START
				
                            ORG 000BH
			ACALL INTERRUPT_0
			RETI
						
				ORG 001BH
INTERRUPT_1:
       PUSH ACC
       PUSH PSW
       CLR TR1
       MOV PSW,#00H
       ACALL KEYPRESSED;       ; to check whether any key is pressed or not
       JNZ CALCULATE           ; if key is pressed then jump to calculate to check is the key     

                               ; pressed is valid key or the previous key is kept pressed till    

                               ; now
       JMP ALTER;              ; If no key is pressed then clear the flag which check whether the 

                               ;  previous key is kept pressed till now

CALCULATE:
       ACALL KEYPRESSED        ; again check whether key is pressed or not
       JZ ALTER                ; if no key is pressed then jump tp clear the flags and start the  

                               ; TIMER 1  again
       ACALL CONVERT           ; if the key is pressed then check the key pressed is a valid key  

                               ; or not depending on the flag FLAG_INVALIDKEY
       JBC FLAG_INVALIDKEY,ALTER ; if this flag is set then the key is invalid and go to ALTER
       ACALL TIMER_0           ;if the key pressed is valid then jump to TIMER 0 for the debounce 

delay
       POP ACC
       POP PSW
       RETI

ALTER:
       CLR FLAG_PUSH           ;clear this flag indicating that the previous key is not being     

                               ; kept pressed and the key which is pressed is now released
AGAIN:
       ACALL TIMER_1           ; call to timer 1 for again scanning the keys
       POP PSW
       POP ACC
       RETI
	
INTERRUPT_0:
       PUSH ACC
       PUSH PSW
       MOV PSW,#00H
       CLR TR0 
       ACALL KEYPRESSED             ;chekh whhether the key is pressed or not again
       JZ ALTER_1                   ;if not pressed then jump to ALTER 1 for clearing the flags   

                                    ; and call to TIMER 1 agan for scanning the key's
       ACALL CONVERT                ;if key is pressed check it is valid or not
       JBC FLAG_INVALIDKEY,ALTER_1  ; invalid key indication if this flag is set
       JB FLAG_PUSH,COMPARE         ; if this flag is found set then it means that the key found  

                                    ; to be pressed is the same key previously kept pressed
       SETB FLAG_PUSH               ; if FLAG_PUSH is not found to be set then it means that the  

                                    ; valid key is a new key
       MOV NEWKEY,A                 ; move this newkey value to the flag NEWKEY
       JMP HOME                     ; jump to home

COMPARE:
        CJNE A,NEWKEY,CLEAR ; if the FLAG_PUSH is found to be set then control comes to this      

                       ; statement for checking whether the key kept pressed for a long time      

                       ; is the previous one or not
        JMP AGAIN_1         ; if it is the same key kept pressed then do nothing and              

                            ; again call to TIMER 1 so that scanning of keys can be done again    

                         ; but dont clear the FLAG_PUSH flag this time because the key kept       

                         ;pressed has not indicated to be released till now

HOME:		
 JB ACC.0,COOL_0; if these bits are ON then it means 
 JB ACC.1,COOL_1; which key is pressed at this moment
 JB ACC.2,COOL_2; and accordingly jump to that 
 JB ACC.3,COOL_3; 
 JB ACC.4,COOL_4
 JB ACC.5,COOL_5
 JB ACC.6,COOL_6
 JB ACC.7,COOL_7

CLEAR:
     CLR FLAG_PUSH   ; If the key being kept pressed is not the same previous key then            

                     ; it means that the previous key kept pressed has been released              

                     ; and this is the new key which is pressed and it is valid ... so            

                     ; jump to HOME
     JMP HOME
			
WORLD:
    MOV R0,A   ; if the key is pressed second time then
    MOV A,P2   ; make the corresponding LED OFF while all
    ORL A,R0   ; other LED's are not been effected at all
    XRL A,R0
    MOV P2,A
    JMP STATUS ;jump to status to CLEAR the flag which indicated the key is being pressed for the 

               ; 1st time or 2nd time
				
UNIVERSE:
    ORL A,P2  ; If the control comes here then it means that the key being pressed is pressed for 

              ; the first time and so the corresponding LED is maked ON
    MOV P2,A
    JMP AGAIN_1

ALTER_1:
    CLR FLAG_PUSH
AGAIN_1:
    ACALL TIMER_1
    POP PSW
    POP ACC
    RET
				
COOL_0:
    JB FLAG_0,WORLD ; if this flag is found to be set then it means the key is being pressed      

                    ;previously and so jump to WORLD for making OFF LED that is corresponding to  

                   ; this key
    SETB FLAG_0     ; set this flag coz the key is pressed fot the 1st time
    JMP UNIVERSE    ; jump to universe to make the corrersponding LED ON

COOL_1:
    JB FLAG_1,WORLD
    SETB FLAG_1
    JMP UNIVERSE

COOL_2:
   JB FLAG_2,WORLD
   SETB FLAG_2
   JMP UNIVERSE
COOL_3:
   JB FLAG_3,WORLD
   SETB FLAG_3
   JMP UNIVERSE
COOL_4:
   JB FLAG_4,WORLD
   SETB FLAG_4
   JMP UNIVERSE

COOL_5:
   JB FLAG_5,WORLD
   SETB FLAG_5
   JMP UNIVERSE
COOL_6:
   JB FLAG_6,WORLD
   SETB FLAG_6
   JMP UNIVERSE
COOL_7:
   JB FLAG_7,WORLD
   SETB FLAG_7
   JMP UNIVERSE


STATUS:
    JBC FLAG_0,AGAIN_1; flag is cleared to make it fresh key
    JBC FLAG_1,AGAIN_1
    JBC FLAG_2,AGAIN_1
    JBC FLAG_3,AGAIN_1
    JBC FLAG_4,AGAIN_1
    JBC FLAG_5,AGAIN_1
    JBC FLAG_6,AGAIN_1
    JBC FLAG_7,AGAIN_1

KEYPRESSED:
    MOV A,P1; as the PORT 1 is made as an input PORT so all the bits are high ... the key pressed 

            ; bit will be low so the value is transfered to ACCUMULATOR for further processing
    CPL A   ; the value in ACC is complimented coz all the bits in PORT 1 are high as it is an    

         ; input port
    RET
			
START:
    MOV IE,#08AH
    MOV TMOD,#011H
    MOV P1,#0FFH; make PORT 1 as an input port
    MOV P2,#00H
    MOV R0,#00H
    MOV R7,#00H
    CLR FLAG_0
    CLR FLAG_1
    CLR FLAG_2
    CLR FLAG_3
    CLR FLAG_4
    CLR FLAG_5
    CLR FLAG_6
    CLR FLAG_7
    ACALL TIMER_1
			
KEY:
    MOV A,P1
    CPL A
    JMP KEY

TIMER_0:
    MOV TL0,#DELAY_LOW
    MOV TH0,#DELAY_HIGH
    SETB TR0
    RET
				
TIMER_1:
    MOV TL1,#0E0H
    MOV TH1,#0B1H
    SETB TR1
    RET
			
CONVERT:
     CLR FLAG_INVALIDKEY ; this subrountine check the validity of the key that is pressed ... and 

                         ; indicates it by the flag FLAG_INALIDKEY				
      CJNE A,#01H,SECOND
      RET
SECOND:
      CJNE A,#02H,THIRD
      RET
THIRD:
     CJNE A,#04H,FOURTH
     RET
						
FOURTH:
     CJNE A,#08H,FIVE
     RET
FIVE:
     CJNE A,#010H,SIX
     RET
SIX:
     CJNE A,#020H,SEVEN
     RET
SEVEN:
     CJNE A,#040H,EIGHT
     RET
EIGHT:
     CJNE A,#080H,BAD
     RET
BAD:
     SETB FLAG_INVALIDKEY
     RET


;************************************************************************************************

**
    END