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
		
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ACALL KEYPRESSED; to check whether any key is pressed or not
		
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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
		
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JMP ALTER; If no key is pressed then clear the flag which check whether the previous key is kept pressed till now

CALCULATE:

		
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ACALL KEYPRESSED; again check whether key is pressed or not 
		
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JZ ALTER; if no key is pressed then jump tp clear the flags and start the TIMER 1 again
		
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ACALL CONVERT; if the key is pressed then check the key pressed is a valid key or not depending on the flag FLAG_INVALIDKEY
		
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JBC FLAG_INVALIDKEY,ALTER; if this flag is set then the key is invalid and go to ALTER 
		
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ACALL TIMER_0; if the key pressed is valid then jump to TIMER 0 for the debounce delay
		
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POP ACC
		
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POP PSW
		RETI
ALTER:
		
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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:

		
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ACALL TIMER_1; call to timer 1 for again scanning the keys
		
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POP PSW
		
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POP ACC
		
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RETI
	
			
INTERRUPT_0:

		
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PUSH ACC
		
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PUSH PSW
		
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MOV PSW,#00H
		
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CLR TR0
		
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ACALL KEYPRESSED; chekh whhether the key is pressed or not again
		
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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
		
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ACALL CONVERT ; if key is pressed check it is valid or not
		
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JBC FLAG_INVALIDKEY,ALTER_1; invalid key indication if this flag is set
		
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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
		
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SETB FLAG_PUSH; if FLAG_PUSH is not found to be set then it means that the valid key is a new key
		
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MOV NEWKEY,A; move this newkey value to the flag NEWKEY
		
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JMP HOME; jump to home
COMPARE:

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

CLEAR:

		
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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
		
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JMP HOME
			
WORLD:

		
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MOV R0,A; if the key is pressed second time then
		
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MOV A,P2; make the corresponding LED OFF while all
		
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ORL A,R0; other LED's are not been effected at all
		
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XRL A,R0
		
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MOV P2,A
		
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JMP STATUS; jump to status to CLEAR the flag which indicated the key is being pressed for the 1st time or 2nd time
				
UNIVERSE:

		
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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
		
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MOV P2,A
		
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JMP AGAIN_1
	
ALTER_1:

		
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CLR FLAG_PUSH

AGAIN_1:

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ACALL TIMER_1

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POP PSW

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POP ACC

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RET

COOL_0:

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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

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SETB FLAG_0; set this flag coz the key is pressed fot the 1st time

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JMP UNIVERSE; jump to universe to make the corrersponding LED ON

COOL_1:

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JB FLAG_1,WORLD

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SETB FLAG_1

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JMP UNIVERSE

COOL_2:

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JB FLAG_2,WORLD

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SETB FLAG_2

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JMP UNIVERSE
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COOL_3:

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JB FLAG_3,WORLD

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SETB FLAG_3

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JMP UNIVERSE

COOL_4:

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JB FLAG_4,WORLD

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SETB FLAG_4

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JMP UNIVERSE

COOL_5:

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JB FLAG_5,WORLD

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SETB FLAG_5

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JMP UNIVERSE

COOL_6:

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JB FLAG_6,WORLD

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SETB FLAG_6

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JMP UNIVERSE

COOL_7:

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JB FLAG_7,WORLD

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SETB FLAG_7

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JMP UNIVERSE

STATUS:

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JBC FLAG_0,AGAIN_1; flag is cleared to make it fresh key

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JBC FLAG_1,AGAIN_1

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JBC FLAG_2,AGAIN_1

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JBC FLAG_3,AGAIN_1

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JBC FLAG_4,AGAIN_1

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JBC FLAG_5,AGAIN_1

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JBC FLAG_6,AGAIN_1

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JBC FLAG_7,AGAIN_1

KEYPRESSED:

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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

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CPL A; the value in ACC is complimented coz all the bits in PORT 1 are high as it is an input port

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RET

START:

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MOV IE,#08AH

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MOV TMOD,#011H

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MOV P1,#0FFH; make PORT 1 as an input port

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MOV P2,#00H

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MOV R0,#00H

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MOV R7,#00H

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CLR FLAG_0

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CLR FLAG_1

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CLR FLAG_2

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CLR FLAG_3

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CLR FLAG_4

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CLR FLAG_5

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CLR FLAG_6

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CLR FLAG_7

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ACALL TIMER_1

KEY:

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MOV A,P1

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CPL A

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JMP KEY

TIMER_0:

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MOV TL0,#DELAY_LOW

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MOV TH0,#DELAY_HIGH

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SETB TR0

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RET

TIMER_1:

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MOV TL1,#0E0H

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MOV TH1,#0B1H

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SETB TR1

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RET

CONVERT:

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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