I have a problem when I send some character from an hyperterminal through an uart frame, I receive the wrong character. I use a PIC 18F46K80. In some test I did, I got these results :

Test 1 :
Character sent : 'A' (=1000001)
Character received : '_' (=01011111)

Test 2 :
Character sent : 'B' (=1000010)
Character received : '/' (=101111)

Test 3 :
Character sent : 'C' (=1000011)
Character received : '^' (=1011110)

I don't know what is the logic of the transmission. You can find bellow my code:

#include <stdio.h>
#include <stdlib.h>
#include <usart.h>
#include <math.h>
#include <p18f46k80.h>

//CPU Configuration
#pragma config FOSC = INTIO1    // internal oscillitor
//#pragma config BOREN = ON       // Enable Brown-out Reset 
#pragma config WDTEN = OFF      // Watchdog timer is disabled
#pragma config XINST = OFF      // CPU Extended mode is disabled

typedef unsigned char bool;
#define true    1
#define false   0

unsigned char msgData[100];
unsigned char cTemp;
unsigned char cTemp_0;

int i=0;

void ports_IO_init();
void init_UART();
void FOSC_Config();
void start_UART();

void main()
    bool b=0;  

    int J=0;
    unsigned char len=0;


       if (PIR1bits.RC1IF==1)
           cTemp = RCREG;

void ports_IO_init()
    TRISCbits.TRISC6 = 0; //Le port RC6 en sortie TX1
    TRISCbits.TRISC7 = 1; //Le port RC7 en entrée RX1

void init_UART()
    //Configuration of TX
    TXSTA1bits.TX9 = 0; //8-Bit Transmit Enable
    TXSTA1bits.TXEN = 1; //Transmit is enabled
    TXSTA1bits.SYNC = 0; // Asynchronous mode
    TXSTA1bits.SENDB = 1; //Sends Sync Break on next transmission
    TXSTA1bits.BRGH = 0; //Baud rate selected at high speed

    //Configuration of RX
    RCSTA1bits.SPEN = 1; //Serial port is enabled
    RCSTA1bits.RX9 = 0; // 8 bits reception
    RCSTA1bits.CREN = 1; //Enable receiving

    //Configuration du bauderate 
    //For a FOSC of 8 MHz, a desired baud rate of 9600, in Asynchronous mode, and 8-bit BRG
    // SBRG1 = ((FOSC/Desired Baude Rate)/64)-1 ((8000000/9600)/64)-1 = 12
     SPBRG1 = 12; // 12 = 0xC in Hex

void FOSC_Config()
    // Configuration for a frequency of 8Mhz
    OSCCONbits.IRCF = 110;
    OSCCONbits.SCS1 = 1;


    OSCTUNEbits.INTSRC= 1;
    OSCTUNEbits.PLLEN = 1;

void start_UART(void)
  • \$\begingroup\$ When posting code, please use the code markup - otherwise your question will look extremely bad. (Should have been visible in the rendered preview on the bottom of your question asking screen) \$\endgroup\$
    – Arsenal
    Oct 8, 2015 at 15:52
  • \$\begingroup\$ First question with serial transmission issues: have you shared the ground between PC and microcontroller? Are you using the same voltage levels? (i.e. not RS232 mixed with TTL UART) I guess you set the baudrate correctly on the PC. \$\endgroup\$
    – Arsenal
    Oct 8, 2015 at 15:56
  • \$\begingroup\$ In Asynchronous mode TXSTA1bits.BRGH = 1; is High Speed \$\endgroup\$
    – Tinez
    Oct 8, 2015 at 16:45

2 Answers 2


It looks like your oscillator is not set up right. Your OSCCON:IRCF bits are 110, so they are giving you a clock of 8MHz, and your baud rate calculation is based on 8MHz. However, you have PLLEN set. This turns on the phase lock loop, producing an effective FOSC frequency of four times 8MHz = 32MHz.

  • \$\begingroup\$ I don't think that there is a problem of the clock configuration: in the PIC datasheet OSCCONbits.IRCF=110 corresponds to frequency of 8MHz. I tried the second solution with setting the clock at 4 MHz and SPBRG at 6, but it still doesn't work. \$\endgroup\$
    – Bicha_95
    Oct 9, 2015 at 8:04
  • \$\begingroup\$ You're right, I was looking at the wrong datasheet. Updated the answer... I still think it's your oscillator speed \$\endgroup\$ Oct 9, 2015 at 14:29

It was a problem of configuration for the baudrate, I set SPBRG1 at 51 and RXDTP (register BAUDCONx) at 1. In any case, thank you all for your help, I which you a nice week :) Aymane


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.