PIC LED flasher
This is my first simple PIC program. It will flash an LED continuously
at approximately 1Hz. It is a very simple loop that delays for 500
milliseconds (half a second) with the LED on, and then delays for
500ms with the LED off. Thus, the LED flashes at 1 Hz!
The schematic for this circuit shows that the
wiring is simple: connect a crystal oscillator across pins 15 and 16
and add the capacitors to ground. Wire a 4k7 resistor to the MCLR
reset pin 4 so the PIC will reset itself at startup. Then connect the
LED via a resistor to pin 17.
When a 4 Mhz cryztal is used with PIC 16C84, the LED will flash at 1 Hz.
This program is available as:
title "Flash - Flash an LED on an off at 1Hz"
; Mark Crosbie 8/22/98
;
; The Program simply sets up Bit 0 of Port "A" to Output and then
; loops, setting the value alternatively low and high
;
; Hardware Notes:
; Reset is tied through a 4.7K Resistor to Vcc and PWRT is Enabled
; A 220 Ohm Resistor and LED is attached to PORTA.0 and Vcc
;
LIST P=16C84, R=DEC
errorlevel 0,-305
INCLUDE "P16C84.inc"
; Registers
Temp equ 12 ; 16 Bit Dlay Variable
__CONFIG _CP_OFF & _WDT_OFF & _XT_OSC & _PWRTE_ON
; Mainline of Flash
org 0
clrf PORTA ; Clear all the Bits in Port "a"
clrf STATUS
bsf STATUS, RP0 ; Goto Bank 1 to set Port Direction
bcf TRISA, 0 ; Set RA0 to Output
bcf STATUS, RP0 ; Go back to Bank 0
Loop
movlw 1 ; Turn on the LED on Port A
movwf PORTA ;
call Dlay ; Delay Before Changing Values
movlw 0 ; Turn off the LED on Port A
movwf PORTA ;
call Dlay ; Delay Before Changing Values
goto Loop
; Dlay Routine - Delay a Half Second before Returning
Dlay
ifndef Debug ; If Debug NOT Defined
movlw 0 ; Actual Setup the Delay Value
movwf Temp
movlw 128
movwf Temp + 1
else ; If Debug Defined
movlw 2 ; Programming Debug Delay Value
movwf Temp
movlw 1
movwf Temp + 1
endif
D_Loop ; Loop Around Here until Complete
decf Temp ; Decrement the lo Value
btfsc STATUS, Z ; Is the Zero Flag Set?
decf Temp + 1
movf Temp, w ; Are we At Zero for Both?
iorwf Temp + 1, w
btfss STATUS, Z
goto D_Loop
return
end
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