why is my PIC MCU sending garbage instead of correct words on the serial port?

Question

I've written a simple code to send some string to pc using PIC18F26K22 MCU. this code works on some other MCUs but on this mcu I get continuous 0xFF on output !.

If I write TXREG2='k' it does work ! but for sending a string it seems that the program stuck on pc_write function because RA0 pin doesn't switch on an off and pc receives continuous 0xFF and never ends !

What am I doing wrong ?!.

Thanks in advance .

this is the code(20 Mhz frequency is previously defined in project properties )

  #pragma config FOSC = HSHP      // Oscillator Selection bits (HS oscillator (high power > 16 MHz))
    #pragma config PLLCFG = OFF     // 4X PLL Enable (Oscillator used directly)
    #pragma config PRICLKEN = ON    // Primary clock enable bit (Primary clock enabled)
    #pragma config FCMEN = OFF      // Fail-Safe Clock Monitor Enable bit (Fail-Safe Clock Monitor disabled)
    #pragma config IESO = OFF       // Internal/External Oscillator Switchover bit (Oscillator Switchover 

mode disabled)

// CONFIG2L
#pragma config PWRTEN = OFF     // Power-up Timer Enable bit (Power up timer disabled)
#pragma config BOREN = SBORDIS  // Brown-out Reset Enable bits (Brown-out Reset enabled in hardware only (SBOREN is disabled))
#pragma config BORV = 190       // Brown Out Reset Voltage bits (VBOR set to 1.90 V nominal)

// CONFIG2H
#pragma config WDTEN = OFF      // Watchdog Timer Enable bits (Watch dog timer is always disabled. SWDTEN has no effect.)
#pragma config WDTPS = 32768    // Watchdog Timer Postscale Select bits (1:32768)

// CONFIG3H
#pragma config CCP2MX = PORTC1  // CCP2 MUX bit (CCP2 input/output is multiplexed with RC1)
#pragma config PBADEN = OFF     // PORTB A/D Enable bit (PORTB<5:0> pins are configured as digital I/O on Reset)
#pragma config CCP3MX = PORTB5  // P3A/CCP3 Mux bit (P3A/CCP3 input/output is multiplexed with RB5)
#pragma config HFOFST = ON      // HFINTOSC Fast Start-up (HFINTOSC output and ready status are not delayed by the oscillator stable status)
#pragma config T3CMX = PORTC0   // Timer3 Clock input mux bit (T3CKI is on RC0)
#pragma config P2BMX = PORTB5   // ECCP2 B output mux bit (P2B is on RB5)
#pragma config MCLRE = EXTMCLR  // MCLR Pin Enable bit (MCLR pin enabled, RE3 input pin disabled)

// CONFIG4L
#pragma config STVREN = ON      // Stack Full/Underflow Reset Enable bit (Stack full/underflow will cause Reset)
#pragma config LVP = ON         // Single-Supply ICSP Enable bit (Single-Supply ICSP enabled if MCLRE is also 1)
#pragma config XINST = ON       // Extended Instruction Set Enable bit (Instruction set extension and Indexed Addressing mode enabled)

// CONFIG5L
#pragma config CP0 = OFF        // Code Protection Block 0 (Block 0 (000800-003FFFh) not code-protected)
#pragma config CP1 = OFF        // Code Protection Block 1 (Block 1 (004000-007FFFh) not code-protected)
#pragma config CP2 = OFF        // Code Protection Block 2 (Block 2 (008000-00BFFFh) not code-protected)
#pragma config CP3 = OFF        // Code Protection Block 3 (Block 3 (00C000-00FFFFh) not code-protected)

// CONFIG5H
#pragma config CPB = OFF        // Boot Block Code Protection bit (Boot block (000000-0007FFh) not code-protected)
#pragma config CPD = OFF        // Data EEPROM Code Protection bit (Data EEPROM not code-protected)

// CONFIG6L
#pragma config WRT0 = OFF       // Write Protection Block 0 (Block 0 (000800-003FFFh) not write-protected)
#pragma config WRT1 = OFF       // Write Protection Block 1 (Block 1 (004000-007FFFh) not write-protected)
#pragma config WRT2 = OFF       // Write Protection Block 2 (Block 2 (008000-00BFFFh) not write-protected)
#pragma config WRT3 = OFF       // Write Protection Block 3 (Block 3 (00C000-00FFFFh) not write-protected)

// CONFIG6H
#pragma config WRTC = OFF       // Configuration Register Write Protection bit (Configuration registers (300000-3000FFh) not write-protected)
#pragma config WRTB = OFF       // Boot Block Write Protection bit (Boot Block (000000-0007FFh) not write-protected)
#pragma config WRTD = OFF       // Data EEPROM Write Protection bit (Data EEPROM not write-protected)

// CONFIG7L
#pragma config EBTR0 = OFF      // Table Read Protection Block 0 (Block 0 (000800-003FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR1 = OFF      // Table Read Protection Block 1 (Block 1 (004000-007FFFh) not protected from table reads executed in other blocks)
#pragma config EBTR2 = OFF      // Table Read Protection Block 2 (Block 2 (008000-00BFFFh) not protected from table reads executed in other blocks)
#pragma config EBTR3 = OFF      // Table Read Protection Block 3 (Block 3 (00C000-00FFFFh) not protected from table reads executed in other blocks)

// CONFIG7H
#pragma config EBTRB = OFF      // Boot Block Table Read Protection bit (Boot Block (000000-0007FFh) not protected from table reads executed in other blocks)

// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.
#include <xc.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h> 


void delay(int x){
 int b=0;   
    for(b=0; b<x;b++){
        
      __delay_ms(1);  
        
    }
}
    

   void pc_write(const char *data) 
{ 
   while(*data){ 
      while (TXSTA2bits.TRMT==0);
       TXREG2=(*data++); 
     }
}


int main() {
   
ANSELA=0;
ANSELB=0;
ANSELC=0;
TRISC=0b11000000;
TRISB=0b11000000; 
TRISA=0X0;
LATA=0;
LATB=0;
LATC=0;
TXSTA1bits.TXEN=1;
TXSTA1bits.SYNC=0;
RCSTA1bits.SPEN=1;
TXSTA2bits.TXEN=1;
TXSTA2bits.SYNC=0;
RCSTA2bits.SPEN=1;
RCSTA1bits.CREN=1;
RCSTA2bits.CREN=1;

TXSTA2bits.BRGH=1; //
BAUDCON2bits.BRG16=0; // 8 bit baud active 
SPBRG2=129;

while (1){
    
 LATAbits.LA0=1;
 delay(500);
 
 pc_write("Test") ; 
 
  LATAbits.LA0=0;
 delay(500);
  
  
}

}

Answer 1

@Hesi I've tried your code in MPLABX simulator. My IDE version is 5.50 and XC8 version is 2.32. But it didn't compiled your original code for the following config:
#pragma config XINST = ON
with this error:

/opt/microchip/mplabx/v5.50/packs/Microchip/PIC18F-K_DFP/1.4.87/xc8/pic/include/proc/pic18f26k22.h:16684:: error: (1504) the PIC18 extended instruction set was enabled but is not supported by this compiler

I then modified the config pragma line as XINST = OFF and it was successfully compiled. It does outputs the characters in the UART window. However in the real physical world there are many things that may affect the MCU's behaviour. I think you connect your circuit to your PC with some sort of RS232 cables and level converters. If so, then make sure that your intermediary equipments connected right and have no problems. There are other several steps you can take to debug your circuit:

• You can debug the TX line of your MCU using an osciloscope
• If it is not possible you can use another MCU to test yours by connecting the lines directly end to end. You can write a test program which reads the UART input and displays it on an character LCD.

By the way is this the same code you are using in your MCU? In a project that I'm working I effectively use an 18F46K22 and its USART2 peripheral to send byte sequences with no problems. This is how I initiate it @16 MHz if it helps:

// BRG16 = 1, BRGH = 1

// disable interrupts before changing states
PIE3bits.RC2IE = 0;
PIE3bits.TX2IE = 0;

// ABDOVF no_overflow; CKTXP async_noninverted_sync_fallingedge; BRG16 16bit_generator; WUE disabled; ABDEN disabled; DTRXP not_inverted; 
BAUDCON2 = 0x08;

// SPEN enabled; RX9 8-bit; CREN enabled; ADDEN disabled; SREN disabled; 
RCSTA2 = 0x90;

// TX9 8-bit; TX9D 0; SENDB sync_break_complete; TXEN enabled; SYNC asynchronous; BRGH hi_speed; CSRC slave_mode; 
TXSTA2 = 0x24;

// 9Fh @9600 bps ve @16 MHz
SPBRG2 = 0x9F;

// 1h @9600 bps ve @16 MHz
SPBRGH2 = 0x01;

// enable receive interrupt
PIE3bits.RC2IE = 1;