Try setting ALL used I/O's  as OUTPUT.


Paulo Ricardo Pabst.


-----Mensagem original-----
De: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]Em nome de Tony Nixon
Enviada em: ter=E7a-feira, 6 de agosto de 2002 19:50
Para: PICLIST@MITVMA.MIT.EDU
Assunto: Re: [PIC][EE]: Unstable circuit


Fredrik Axtelius wrote:
>
> Hi!!
>
> I have a PIC16F877 circuit and im having big problems to get it stable.

Disable WDT
Disable LVP
Check crystal circuit, Vss connection to it, keep it compact and near
the chip
Wrong OSC fuse setting, try HS mode
Floating inputs
Disconnect PC from circuit
Tie MCLR hard to 5V
Verify software
Delete all software except for "flashy LED"
Check ground rails in circuit
Connect BOTH Vdd and Vss to power supply
Use another 877 chip
Verify programming
Change power supplies
Check circuit for dry joints & shorted IO pins
Try LED on another IO pin
Check for BSF instructions on PORTS
Give me $10, that helps


Try this, it works..


        list p=3D16f877   ; processor type

        #include "p16f877.inc"
;
; ------------------
; CONFIGURATION FUSE
; ------------------
;
        __CONFIG _CP_OFF & _WRT_ENABLE_OFF & _HS_OSC & _WDT_OFF & _PWRTE_=
OFF
&
_BODEN_OFF & _LVP_OFF & _CPD_OFF & _DEBUG_OFF
;
; The purpose of this program is to make a LED turn on and off
; The LED is connected to PortB any pin
; The flash rate is 500mS @ 4MHz
;

        CBLOCK 0x20
DelayL          ; delay register LOW byte
DelayM          ; delay register MID byte
DelayH          ; delay register HIGH byte
        ENDC

;
; -------------
; PROGRAM START
; -------------
;
        org 0h                  ; startup address =3D 0000


        clrf PORTA
        clrf PORTB
        clrf PORTC
        clrf PORTD
        clrf PORTE
        bsf Status,RP0          ; set RP0 for RAM page 1
        clrf TrisA              ; all PortA =3D outputs
        clrf TrisB              ; all PortB =3D outputs
        clrf TrisC              ; all PortC =3D outputs
        clrf TrisD              ; all PortD =3D outputs
        clrf TrisE              ; all PortE =3D outputs
;
; -------------------------
; SET ANALOG/DIGITAL INPUTS
; -------------------------
;
        movlw b'00000110'       ; all digital
        movwf ADCON1
        bcf Status,RP0          ; set RP0 for RAM page 0


start   clrf PORTB
        call Delay500           ; execute a 500mS delay

        movlw 0xFF
        movwf PORTB
        call Delay500           ; execute a 500mS delay
        goto start              ; do this loop forever
;
; ---------------------------------------
; SUBROUTINE: waste time for 500mS @ 4MHz
; ---------------------------------------
;

Delay500 clrf DelayL            ; clear DelayL to 0
        clrf DelayM             ; clear DelayM to 0
        movlw 3h                ; set DelayH to 3
        movwf DelayH
Wait1   decfsz DelayL           ; subtract 1 from DelayL
        goto Wait1              ; if not 0, goto Wait1
        decfsz DelayM           ; subtract 1 from DelayM
        goto Wait1              ; if not 0, goto Wait1
        decfsz DelayH           ; subtract 1 from DelayH
        goto Wait1              ; if not 0, goto Wait1
        return                  ; finished the delay

                end


--
Best regards

Tony

mICros
http://www.bubblesoftonline.com
mailto:sales@bubblesoftonline.com

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