LED flasher using PIC16C84 Microcontroller

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:

• flash.asm source code
• flash.jpg schematic

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

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