// 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 - Full duplex - Master

#include "ConfigurationBits.h"

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

//#define MAX146_CONTROL_BYTE 0x8F // 1000 1111 = Channel 0, Unipolar, single ended, external clock (see datasheet)
#define MAX146_CONTROL_BYTE 0xCF // 1100 1111 = Channel 0, Unipolar, single ended, external clock (see datasheet)

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

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

void main(void) {

    unsigned short int Byte1, Byte2, dummy;

    // 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 - Unused
    TRISBbits.RB1 = 0; // Set SS1 pin as output
    TRISCbits.RC4 = 1; // Set MISO pin as input


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

    CLK = 0; // Clear clock

    while (1) {
        SS1 = 0; // Enable Slave Select (ADC)

        dummy = SPI_Master_write_read_byte(MAX146_CONTROL_BYTE); // Write a byte to slave - Read back firs byte
        __delay_us(20); // Useless delay...
        Byte1 = SPI_Master_write_read_byte(0); // Write 0 to slave - Read a byte
        __delay_us(20); // Useless delay...
        Byte2 = SPI_Master_write_read_byte(0); // Write 0 to slave - Read a byte

        SS1 = 1; // Disable Slave Select (ADC)

        __delay_ms(10);
    }
}

unsigned char SPI_Master_write_read_byte(unsigned char dato) {
    unsigned char mask;
    unsigned char data = 0;

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

        __delay_us(10); // Delay half periode
        CLK = 1; // Clock active on rising edge

        if (MISO)
            data = data | mask;

        __delay_us(10); // Delay half periode
        CLK = 0; // Clock to idle
    }
    return data;
}