Here an LED connected to the first pin of port0 (P0.0) is blinked continuously. The assembly program given below is simple and self explanatory.
;*************************************************
;
;Program: Blinking LED.
;Author: Srikanth
;Website: http://shree-electronics.com/
;Description: Blinks an LED connected to P0.0
;continuously
;
;*************************************************
led equ P0.0
org 00h
up: setb led ;Turn ON the LED
acall delay ;call delay subroutine
clr led ;Turn OFF the LED
acall delay ;call delay subroutine
sjmp up ;Loop
delay:mov r7,#0ffh ;delay subroutine
loop:mov r6,#0ffh
djnz r6,$
djnz r7,loop
ret
end