// PIC18 in C - Versione 0.2 - Febbraio 2015
// Copyright (c) 2015, Vincenzo Villa
// Creative Commons | Attribuzione-Condividi allo stesso modo 3.0 Unported.
// Creative Commons | Attribution-Share Alike 3.0 Unported
// https://www.vincenzov.net/tutorial/PIC18/SPI.htm

// PIC18F25K20 / MPLABX 2.30 / XC8 1.33
// Software SPI - Write only master

#include "ConfigurationBits.h"

#define _XTAL_FREQ 1000000 // Default output frequency of HFINTOSC at Reset

#define DATA1 0x78  // See MCP4822 data sheet -> Write 0x85A to DAC A
#define DATA2 0x5A  // See MCP4822 data sheet -> Write 0x85A to DAC A 

#define MOSI LATCbits.LATC5 // Pin 16 MOSI RC5/SDO
#define MISO LATCbits.LATC4 // Pin 15 MISO RC4/SDI - Unused
#define SS0  LATBbits.LATB0 // Pin 21 DAC_SS RB0
#define SS1  LATBbits.LATB1 // Pin 22 ADC_SS RB1 - Unused
#define CLK  LATCbits.LATC3 // Pin 14 SCK RC3/SCK

// Write a byte to SPI - Master
void SPI_Master_write_byte(unsigned char dato);

void main(void) {

    // Configure SPI pin
    TRISCbits.RC5 = 0; // Set MOSI pin as output
    TRISCbits.RC3 = 0; // Set clock pin as output
    TRISBbits.RB0 = 0; // Set SS0 pin as output
    TRISBbits.RB1 = 0; // Set SS1 pin as output - Unused
    TRISCbits.RC4 = 1; // Set MISO pin as input - Unused

    SS0 = 1; // Disable Slave Select (DAC)
    SS1 = 1; // Disable Slave Select (ADC) - Unused

    CLK = 0; // Clear clock

    while (1) {
        SS0 = 0; // Enable Slave Select (DAC)

        SPI_Master_write_byte(DATA1); // Write a byte to slave
        __delay_us(200); // Useless delay...
        SPI_Master_write_byte(DATA2); // Write a byte to slave

        SS0 = 1; // Disable Slave Select (DAC)

        __delay_ms(10);
    }
}

void SPI_Master_write_byte(unsigned char dato) {
    unsigned char mask;

    for (mask = 0x80; mask != 0; mask >>= 1) { // Write 8 bit, starting form MSB
        if (dato & mask) // If masked bit is 1
            MOSI = 1; // Write single 1
        else
            MOSI = 0; // Write single 0

        __delay_us(100); // Delay half periode
        CLK = 1; // Clock active on rising edge
        __delay_us(100); // Delay half periode
        CLK = 0; // Clock to idle
    }
}