How I got serial working on a PIC18F2550

main.c

/*
 * File:   main.c
 * Author: max
 *
 * Created on April 14, 2018, 10:40 AM
 */

// Set the OSC to internal osc which is 8 MHz
#pragma config FOSC = INTOSC_EC
#pragma config WDT = OFF // turn off watch dog
#pragma config BOR = OFF // turn off brown out reset because my wiring SUCKS and the circuit's voltage varies with my mood...
#pragma config PBADEN = OFF // turn off ADC converter
#pragma config LVP = OFF
/// ^^^^^ Long story about this ^^^^^^
// You do this if you have a high voltage programming capable programmer, if you don't, tie PGM low with >10K ohm resistor
// Why? because if you leave PGM floating, with LVP, you'll waste many hours troubleshooting the random crashes
// floating PGM w/ LVP is akin to leaving MCLR or on AVR, RESET line floating :)
// 
// Massive thank you to -> https://electronics.stackexchange.com/a/30449

// Have to set this constant so stuff like __delay_ms() knows our clock speed
#define _XTAL_FREQ 8000000

// Usual includes
#include <xc.h>
#include <string.h>

// My flail send string function
void tx_str(const char * s)
{
    // This is junk, because it's blocking, kinda defeats the purpose
    // of asynchronous serial...
    // ... but hey it works and I am not ready to torture myself with
    // interrupt vectors **yet**
    for(unsigned int i = 0; i < strlen(s); i++)
    {
        // Fill the TXREGister with our delicious bits
        TXREG = s[i];
        
        // aaaand wait for it to drain...
        while(TRMT != 1 && TXIF != 1) {}
    }
}

void main(void) {
    // Set up the clock... otherwise stuff doesn't work
    // Internal OSC Freq Select, 111 = 8 MHz
    IRCF2 = 1; IRCF1 = 1; IRCF0 = 1;
    
    // Init the serial port IO pins
    TRISC7 = 1;
    TRISC6 = 0;
    
    //*
    // 8bit, async mode, tx enabled
    TXSTA = 0; // first we clear the register
    TXEN = 1; // then enable transmission (rest stays 0)
    
    // 8bit, async, rx enabled
    RCSTA = 0; // again nuke the register
    SPEN = 1;
    
    // Baud rate = 9600 baud (act 9616)
    BRG16 = 0; // 8 bit (legacy) baudrate spec
    SPBRG = 12; // 9k12 baud @ 8MHz
    
    // */
    
    // Init our status led
    TRISB0 = 0;
    
    while(1)
    {
        // Hello world, because I am too stupid/tired to come up with something more creative :)
        tx_str("hello world!");
      
        // Flash the LED to prove the uC hasn't had it's RST line dragged low by the stupid pickit3...
        RB0 = ! RB0;
      
        // Sleep for a bit, so I can admire my handy work (:
        __delay_ms(1000);
    }
}