// PIC18 in C - Versione 0.21 - 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
// Hardware 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 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_MSSP(unsigned char dato);

void main(void) {

    unsigned char 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

    // Configure SPI hardware
    SSPCON1bits.SSPEN = 1; //  Synchronous Serial Port Enable bit
    SSPCON1bits.SSPM = 0b0000; // SPI Master mode, clock = FOSC/4
    SSPSTATbits.CKE = 1; // 1 = Transmit occurs on transition from active to Idle clock state
    SSPCON1bits.CKP = 0; // Idle state for clock is a low level
    SSPSTATbits.SMP = 0; // Input data sampled at middle of data output time

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

        dummy = SPI_Master_write_read_byte_MSSP(MAX146_CONTROL_BYTE); // Write a byte to slave - Read back 0
        Byte1 = SPI_Master_write_read_byte_MSSP(0); // Write 0 to slave - Read first byte
        Byte2 = SPI_Master_write_read_byte_MSSP(0); // Write 0 to slave - Read first byte

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

        __delay_ms(10);
    }
}

unsigned char SPI_Master_write_read_byte_MSSP(unsigned char dato) {
    SSPBUF = dato; // Send 8 bit to SPI
    while (!SSPSTATbits.BF); // SSPBUF is empty?
    return SSPBUF;
}