8051 Program – down counter 8bit

; down counter 8bit
; counts from 255 to 0
	ORG 0H
	COUNT_FROM EQU 100
MAIN:
	LCALL COUNT
	SJMP MAIN
COUNT:
	MOV A,#COUNT_FROM	;load COUNT_FROM in A
down:	MOV P0,A	;move data from a to port0
	ACALL delay	;call delay routine
	DEC A	;decrement a
	CJNE A,#0,up	;compare a with 0, if not equal, jump to location up
	RET
;delay routine
delay:
	MOV R1,#0FFH	;move 0ffh to r1
l3:	MOV R2,#0FFH	;move 0ffh to r2
l2:	MOV R3,#0FFH	;move 0ffh to r3
l1:	DJNZ R1,l1	;decrement r1, repeat till r1=0
	DJNZ R3,l2	;decrement r3,repeat l2 till r3=0
	DJNZ R2,l3	;decrement r2, repeat l3 till r2=0
	RET
	END

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List of topics: 8051

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