PIC18F4550 Pinout and Pin Configuration

#include <xc.h>

// Configuration Bits
#pragma config FOSC = HSPLL_HS // Using HS oscillator with PLL
#pragma config WDT = OFF        // Watchdog Timer disabled
#pragma config LVP = OFF        // Low-Voltage Programming disabled

#define _XTAL_FREQ 48000000UL   // Define crystal frequency for delay functions

void main(void) {
    // It's good practice to set analog pins to digital
    // if you're not using them for analog functions.
    // 0x0F makes all AN pins digital.
    ADCON1 |= 0x0F;
    
    // Set RD0 pin of PORTD as an output. 0 = output, 1 = input.
    TRISDbits.TRISD0 = 0;
    
    while(1) {
        // Toggle the state of the RD0 pin (blink an LED)
        LATDbits.LATD0 = ~LATDbits.LATD0;
        
        // Delay for 500 milliseconds
        __delay_ms(500);
    }
    return;
}

#include <xc.h>
#define _XTAL_FREQ 48000000UL

// Function Prototypes
void UART_Init(long baudrate);
void UART_Write_Char(char data);
char UART_Read_Char();

void main(void) {
    UART_Init(9600); // Initialize UART at 9600 baud

    while(1) {
        UART_Write_Char('A'); // Transmit character 'A'
        __delay_ms(1000);
    }
}

void UART_Init(long baudrate) {
    // Formula from datasheet for SPBRG calculation
    // N = (Fosc / (16 * Baudrate)) - 1, for BRGH=1
    int n = (_XTAL_FREQ / (16 * baudrate)) - 1;

    if (n < 0) n = 0;

    SPBRG = n; // Set baud rate
    TXSTAbits.BRGH = 1;  // High-speed baud rate mode
    BAUDCONbits.BRG16 = 0; // Use 8-bit baud rate generator

    // Configure TX/RC pins
    TRISCbits.TRISC6 = 0; // TX pin as output
    TRISCbits.TRISC7 = 1; // RX pin as input

    // Enable EUSART module
    TXSTAbits.SYNC = 0;  // Asynchronous mode
    RCSTAbits.SPEN = 1;  // Enable serial port
    TXSTAbits.TXEN = 1;  // Enable transmission
    RCSTAbits.CREN = 1;  // Enable continuous reception
}

void UART_Write_Char(char data) {
    while(!TXSTAbits.TRMT); // Wait until the transmit shift register is empty
    TXREG = data; // Send the data
}

char UART_Read_Char() {
    while(!PIR1bits.RCIF); // Wait for the receive buffer to be full
    return RCREG; // Read the received data
}

#include <xc.h>

// Define a constant string in program memory (ROM)
const char my_rom_message[] = "Hello from ROM!";

void main(void) {
    char data_from_rom;
    
    // UART should be initialized here to display the result
    // UART_Init(9600);

    for (int i = 0; my_rom_message[i] != '\0'; i++) {
        // Set the table pointer to the address of the character
        TBLPTR = (unsigned long)&my_rom_message[i];

        // Execute the table read instruction.
        // The post-increment `*+` is useful for reading sequential bytes.
        asm("TBLRD*");

        // The read data is now in the TABLAT register
        data_from_rom = TABLAT;

        // Transmit the read character via UART
        // UART_Write_Char(data_from_rom);
    }
    
    while(1); // Loop forever
}