#include <xc.h>
#include <stdint.h>
#include <stdbool.h>

#define _XTAL_FREQ 48000000UL

#define RS485_READ 1
#define RS485_WRITE 0
#define IOF_8MHz 0b111
#pragma config XINST = OFF

void clockInit(void);
uint8_t high8(uint16_t x);
uint8_t low8(uint16_t x);

void main(void) {

    clockInit();

    // disables analog-to-digital conversion
    // (enables digital IO on all AD pins)
    ANCON0 = 0x1F;
    ANCON1 = 0x1F;

    // enables rs485 write (output)
    TRISAbits.TRISA2 = 0;

    TXSTA1bits.SYNC = 0;
    TXSTA1bits.BRGH = 1; // set BRGH bit
    TXSTA1bits.TXEN = 1; // enable TX

    RCSTA1bits.SPEN = 1;
    RCSTA1bits.CREN = 1;

    TRISCbits.TRISC6 = 0;
    TRISCbits.TRISC7 = 1; // Rx1 set input

    BAUDCON1bits.BRG16 = 1; // set 16 bits SPBRG
    BAUDCON1bits.RCIDL = 1; // set receive active

    SPBRGH1 = high8(104); // set UART speed SPBRGH
    SPBRG1 = low8(104); // set UART speed SPBRGL

    CM1CONbits.CON = 0; // disables comparator


    /* Loop forever */
    while (1) {
        LATAbits.LATA2 = RS485_WRITE;

        TXREG1 = 0x55; // yes, send char
        while (!TXSTA1bits.TRMT); // Ready ?

        LATAbits.LATA2 = RS485_READ;
        __delay_us(100);
    }
}

/*----------------------------------------------------------------------------*/
void clockInit(void) {
    // disables reference oscillator output
    REFOCONbits.ROON = 0;

    // device enters IDLE mode on SLEEP instruction
    OSCCONbits.IDLEN = 1;
    // system clock is from primary oscillator
    OSCCONbits.SCS = 0;
    // selects base frequency as 8MHz
    OSCCONbits.IRCF = IOF_8MHz;
    // wait until oscillator is running
    while (!OSCCONbits.OSTS);

    // low speed USB (6MHz clock)
    UCFGbits.FSEN = 0;

    // enable PLL
    OSCTUNEbits.PLLEN = 1;
}

uint8_t high8(uint16_t x) {
    return (uint8_t) (x >> 8);
}

uint8_t low8(uint16_t x) {
    return (uint8_t) (x & 0xFF);
}