LED Blinking
The purpose of this example is not to demonstrate the operation of
LEDs, but the operating speed of the microcontroller. Simply put, in
order to enable LED blinking to be visible, it is necessary to provide
sufficient amount of time to pass between on/off states of LEDs. In this
example time delay is provided by executing a subroutine called
Delay.
It is a triple loop in which the program remains for approximately 0.5
seconds and decrements values stored in registers R0, R1 or R2. After
returning from the subroutine, the pin state is inverted and the same
procedure is repeated...
;************************************************************************
;* PROGRAM NAME : Delay.ASM
;* DESCRIPTION: Program turns on/off LED on the pin P1.0
;* Software delay is used (Delay).
;************************************************************************
;BASIC DIRECTIVES
$MOD53
$TITLE(DELAY.ASM)
$PAGEWIDTH(132)
$DEBUG
$OBJECT
$NOPAGING
;STACK
DSEG AT 03FH
STACK_START: DS 040H
;RESET VECTORS
CSEG AT 0
JMP XRESET ;Reset vector
ORG 100H
XRESET: MOV SP,#STACK_START ;Define Stack pointer
MOV P1,#0FFh ;All pins are configured as inputs
LOOP:
CPL P1.0 ;Pin P1.0 state is inverted
LCALL Delay ;Time delay
SJMP LOOP
Delay:
MOV R2,#20 ;500 ms time delay
F02: MOV R1,#50 ;25 ms
F01: MOV R0,#230
DJNZ R0,$
DJNZ R1,F01
DJNZ R2,F02
END ;End of program
