PIC Microcontoller Input / Output LED Methods

Tony Nixon [sales at picnpoke.com] of ICmicro's says:

This program will flash a LED from port pin RC4

RC4 -> Led Anode
Led Cathode -> 1K res
1K res -> ground

;
        Title "LED flasher."
;
        list P = 16F877
;
        include "P16f877.inc"  ; use definition file for 16F877
;
; --------------------
; USER RAM DEFINITIONS
; --------------------
;
        CBLOCK 0x20   ; RAM starts at address 20h
NaHi
NaLo
NbHi
NbLo
        ENDC
;
        org 0x0000      ; start address = 0000h

; INITIALISE PORTS
; binary used to see individual pin level

        movlw b'00000000'       ; all port pins = low
        movwf PORTA
        movlw b'00000000'
        movwf PORTB
        movlw b'00000000'
        movwf PORTC
        movlw b'00000000'
        movwf PORTD
        movlw b'00000000'
        movwf PORTE

        bsf STATUS,RP0  ; set RAM Page 1 for TRIS registers

; INITIALISE PORTS
; binary used to see individual pin IO status

        movlw b'00000000'       ; all IO pins = outputs
        movwf TRISA
        movlw b'00000000'
        movwf TRISB
        movlw b'00000000'
        movwf TRISC
        movlw b'00000000'
        movwf TRISD
        movlw b'00000000'
        movwf TRISE

        movlw b'00000110'       ; all analog pins = digital
        movwf ADCON1

        bcf STATUS,RP0  ; back to RAM page 0

; LED FLASH LOOP

Loop    bsf PORTC,4     ; RC4 = high = led on
        call Delay

        bcf PORTC,4     ; RC4 = low = led off
        call Delay
        goto Loop

; 1/2 SEC DELAY SUBROUTINE WITH 4MHz CLOCK

Delay   movlw 01h
        movwf NbHi
        movlw 03h
        movwf NbLo
        movlw 8Ah
        movwf NaHi
        movlw 5Bh
        movwf NaLo

DeLoop0 decfsz NaLo,F
        goto DeLoop0
        decfsz NaHi,F
        goto DeLoop0
        decfsz NbLo,F
        goto DeLoop0
        decfsz NbHi,F
        goto DeLoop0
        ;
        return

        end

Questions:

• gav_28 at hotmail.com asks:

  Hi, i too am new to programming pics. im trying to program the PIC16F877 to be a realtime clock and to output the time on an LCD display (pref 4 bit to the LCD) if anyone has code or knows where i can find an exmaple of a real time clock i would be so grateful. Im using MPlab to program so assmelby language rather than C or Basic, many thanks

• tigrot at onvol.net asks:

  hi!
  i am a newbie in programming pics,the only pic that i have programmed is the 16F84.now i wish to move to a greater stuff - pic 16F877.Can someone PLEASE send me some good tutorial sites?
  
  Thank You
  

  James Newton replies: See piclist.com/techref/microchip/begin.htm+

  +

• branvan2k at yahoo.es asks:

  i'm a beginner in pic's programming, i say so because my question may sound silly, but here it comes, which electronics i need to make it up? Do you have the design?

  Check the data sheet for the processor clock and power, then just add a 1Kohm resistor and LED between the IO pin to ground.

Comments:

• BE AWARE !!!
  
  There is a mistake in the code. It should be "org 0x0020" instead of "org 0x0000". The way it is now it will not even build.
  
  Daniel+
• livewire at telusplanet.net

  Found a formula to apply your delay routine to. It may not be 100% accurate, but it is really close. (12/Clock Frequency) = Delay/Steps Where steps are offset by 1. Such that 16Mhz clock would provide a delay of 750ms per step. If you required a delay of 500ms, you would need 666,666 steps. Convert 666,666 to Hex and you get 00 0A 2C 2A. Enter these values offset by 1, and you get NaHi=0x2D NaLo=0x2B NbHi=0x01 NbLo=0x0B Works for me.

  +

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