PIC16F-SPI-SLAVE-MAIN.C

// Interrupt Service Routine
void __interrupt() ISR(void)
{
    if(SSPIF)
    {
        Data = SSPBUF;  // Read the received data from the buffer
        SSPIF = 0;      // Clear the interrupt flag
    }
}

// Main Function
void main(void)
{
    SPI_Slave_Init(); // Initialize SPI in slave mode
    TRISB = 0x00;     // Set PORTB as output to display received data

    while(1)
    {
        // Display the received data on PORTB
        PORTB = Data;
    }

    // Return statement included to avoid compilation warnings. Not required in practice due to infinite loop.
    return;
}

// Function to Initialize SPI in Slave Mode
void SPI_Slave_Init(void)
{
    // Set SPI mode to Slave with SS enabled
    SSPM0 = 0;
    SSPM1 = 0;
    SSPM2 = 1;
    SSPM3 = 0;

    // Enable the synchronous serial port
    SSPEN = 1;

    // Configure the clock polarity and phase (SPI Mode 1)
    CKP = 0;
    CKE = 0;

    // Clear the SMP bit
    SMP = 0;

    // Configure the I/O pins for SPI slave mode
    TRISC5 = 0; // SDO -> Output
    TRISC4 = 1; // SDI -> Input
    TRISC3 = 1; // SCK -> Input
    PCFG3 = 0;  // Set SS (RA5/AN4) to be digital I/O
    PCFG2 = 1;
    PCFG1 = 0;
    PCFG0 = 0;
    TRISA5 = 1; // SS -> Input

    // Enable SPI interrupt
    SSPIE = 1;
    PEIE = 1;
    GIE = 1;
}

// Function to Read Data from SPI Buffer
uint8_t SPI_Read(void)
{
    uint8_t data = 0;
    if(BF) // Check if any new data is received
    {
        data = SSPBUF;  // Read the buffer
        BF = 0;         // Clear the buffer-full indicator bit
        SSPIF = 0;      // Clear the interrupt flag bit
        SSPOV = 0;      // Clear the overflow indicator bit
    }
    return data;
}