Electrical – Serial port framing error

mplabxpicpic16fserialuart

I'm new to pic and uart. Just trying out simple uart transmission. I'm using mplab IDE and coolterm for serial monitoring. I'm getting serial framing error.
I also used PuTTY and it was printing junk value. Below's the code that i'm using and i want to print hello world on desktop.

config.h

#ifndef CONFIG_H
#define CONFIG_H

// PIC16F886 Configuration Bit Settings

// 'C' source line config statements

// CONFIG1
#pragma config FOSC = HS        // Oscillator Selection bits (HS oscillator: High-speed crystal/resonator on RA6/OSC2/CLKOUT and RA7/OSC1/CLKIN)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled and can be enabled by SWDTEN bit of the WDTCON register)
#pragma config PWRTE = ON       // Power-up Timer Enable bit (PWRT enabled)
#pragma config MCLRE = ON       // RE3/MCLR pin function select bit (RE3/MCLR pin function is MCLR)
#pragma config CP = OFF         // Code Protection bit (Program memory code protection is disabled)
#pragma config CPD = OFF        // Data Code Protection bit (Data memory code protection is disabled)
#pragma config BOREN = ON       // Brown Out Reset Selection bits (BOR enabled)
#pragma config IESO = ON        // Internal External Switchover bit (Internal/External Switchover mode is enabled)
#pragma config FCMEN = ON       // Fail-Safe Clock Monitor Enabled bit (Fail-Safe Clock Monitor is enabled)
#pragma config LVP = OFF        // Low Voltage Programming Enable bit (RB3 pin has digital I/O, HV on MCLR must be used for programming)

// CONFIG2
#pragma config BOR4V = BOR40V   // Brown-out Reset Selection bit (Brown-out Reset set to 4.0V)
#pragma config WRT = OFF        // Flash Program Memory Self Write Enable bits (Write protection off)

#endif  /* CONFIG_H */

uart.c

#include <xc.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<conio.h>
#include "config.h"

#define _XTAL_FREQ 20000000
#define baud 9600

void usart_init();
void usart_send_byte(char);
void usart_send_string(char*);


void usart_init(){
    TRISC6=0;
    TRISC7=1;
//    SPBRG=_XTAL_FREQ/(64*baud) -1;
    SPBRG=31;
    TXSTAbits.BRGH=1;
    TXSTAbits.SYNC=0;
    RCSTAbits.SPEN=1;
    TXSTAbits.TXEN=1;
    RCSTAbits.CREN=1;
    TXSTAbits.TX9=0;
    RCSTAbits.RX9=0;
    RCSTAbits.FERR = 0;     // Disable framing error
    RCSTAbits.OERR = 0;     // Disable overrun error
}

void usart_send_byte(char bt){
    while(TXIF==0);
    TXREG=bt;
}


void usart_send_string(char* str) {
    while(*str!= '\0')
        usart_send_byte(*str++);
}


void main(void) {
    char* str = "Hello world!\n\r";
    usart_init();

    while (1) {
        usart_send_string(str);
        __delay_ms(500);
    }

    return;
}

Best Answer

Your actual baud rate with those settings is 38400. If TXSTAbits.BRGH == 1, then the multiplier is 16, not 64. If you want 9600, then either set TXSTAbits.BRGH = 0 or SPBRG = 129 (20MHz / (16 * 9600))-1.

See the EUSART chapter of the datasheet for more details.

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