8051 Program – timer interrupt based led blinking

; timer interrupt based led blinking
; 8051 with 12Mhz crystal
; led is connected to P1.0
	ORG 0H
	led EQU P1.0
	delay EQU 30h	;ram location
	time EQU 20	;20 x 0.05 = 1 sec
START:	AJMP MAIN	;jump to main program
	ORG 0BH
	AJMP TIMER0_ISR	;jump to interrupt subroutine
MAIN:
init:
	SETB EA	;enable interrupt
	SETB ET0	;enable timer 0 interrupt
	MOV delay,#time
	MOV TMOD,#01h	;timer 0 mode 1(16 bit mode)
	MOV TH0,#3ch	;0.05 sec
	MOV TL0,#0b8h
	SETB TR0	;Start Timer 0
toggle:
	SETB led	; turn on led
	ACALL WAIT	; wait for a second
	CLR led	; trun off led
	ACALL WAIT	; wait for a second
	SJMP toggle	; repeat
	SJMP MAIN
WAIT:	MOV R0,#delay
	CJNE @R0,#time,WAIT
	MOV @R0,#0
	RET
TIMER0_ISR:
	PUSH ACC
	PUSH B
	PUSH PSW
	PUSH DPH
	PUSH DPL
	PUSH 00h	; R0
	INC delay	; increment delay count
	CLR TF0	;clear TIMER 0 flag
	CLR TR0	;stop Timer 0
	MOV TH0,#3ch	;0.05 sec, reload timer
	MOV TL0,#0b8h
	SETB TR0	;Start Timer 0
	POP 00h	;R0
	POP DPL
	POP DPH
	POP PSW
	POP B
	POP ACC
	RETI
	END

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