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Problem with RS232 link with a 12F675

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I'am trying some programming with a 12F675 ...


I have the following test code:


#include <system.h>
#include "main.h"

//Config de la liason série
#pragma RS232_RXPORT GPIO
#pragma RS232_TXPORT GPIO
#pragma RS232_RXPIN 4
#pragma RS232_TXPIN 5
#pragma RS232_BAUD 4800
#pragma TRUE_RS232 1
#pragma CLOCK_FREQ 4000000

#define CR 0x0d //Retour Chariot

//Message de Bienvenue.
const char* bienvenue   = " Convertisseur: \0";

//Define device config block
list p=PIC12F675
__config H'31C4'	

// Interrupt handler
void interrupt( void )

// Main program entry
//Il faut charger la calibration de l'horloge interne:
asm {
 bsf STATUS, RP0
 call 3FFh
 movwf OSCCAL

//Init interrupt registers
//!!! Sample interrupt initialization, correct for your application needs
option_reg = 7; 	 // set prescaler to 1:256

//Init ports
cmcon = 00000111b;  //Comparateur désactivé.
set_bit(trisio, 0); 	 //GP0 input  ->Mesure
set_bit(trisio, 1); 	 //GP1 input  ->Vref
clear_bit(trisio, 2);	//GP2 output ->LED
set_bit(trisio, 4); 	 //GP4 input  ->RS232-RX
clear_bit(trisio, 5);	//GP5 output ->RS232-TX
gpio = 0;    //Init à 0

//Config du CAN

clear_bit(adcon0, ADFM);	//On veut les 8 MSB
set_bit(adcon0, VCFG);  //On utilise VREF
clear_bit(adcon0, CHS0);	// C le channel 0 qui nous intéresse.
clear_bit(adcon0, CHS0);	
set_bit(adcon0, ADON);  //On active le convertisseur

clear_bit(ansel, ADCS2);	// On numérise à la cadence de l'oscillateur interne
set_bit(ansel, ADCS1);
set_bit(ansel, ADCS0);
clear_bit(ansel, ANS3);  //AN3 désactivé
clear_bit(ansel, ANS2);  //AN2 désactivé
set_bit(ansel, ANS1);  //AN1 activé
set_bit(ansel, ANS0);  //AN1 activé

//On affiche le message de Bienvenue.

char i=0;
set_bit(adcon0, GO);  //on lance la capture
while(1) {
 while( (adcon0 & 2) != 0 )
 set_bit(gpio, 2);
 clear_bit(gpio, 2);
 set_bit(adcon0, GO);  //on lance la capture






I have met some problem: For example, I need to put a delay after each putchar command, in order to avoid garbage display on the terminal... is it normal ????


in the main loop ... while (1)....

The putchar command don't have any effect... Can you give a clue of the reason....


Thank you for reading me... and for your help!!

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I was wondering: Is the internal oscillator exact enough to do 9600 RS232 I/O at all?

Clock accuracy is not highly important with RS232 comms, because of its asynchronous nature.

This means that the receiver will resync on every piece of data, that why there are start bits.

As long as the clock is accurate to within 5% or less you should be OK.




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