// Usare il PIC16 come periferica I2C - Versione 0.1 - Gennaio 2010
// Copyright © 2009, VincenzoV.net (https://www.vincenzov.net)
// Creative Commons | Attribuzione-Condividi allo stesso modo 3.0 Unported.
// Creative Commons | Attribution-Share Alike 3.0 Unported
// https://www.vincenzov.net/tutorial/elettronica-di-base/PIC16F690

#include <htc.h>

#define _XTAL_FREQ 8000000
#define I2C_ADDR 0x51

int i2c_counter;

__CONFIG(INTIO &       // Use internal clock
         WDTDIS &      // Disable watchdog
         PWRTEN &      // Delay after power on enabled
         MCLRDIS &     // Internal External Switch Over Mode Disable
         UNPROTECT &   // Disable memory protection
         BORDIS &      // Disable reset on low volage
         IESODIS &     // Internal External Switch Over Mode Disable
         FCMDIS);      // Disable Fail clock monitoring

void main(void) 
{OSCCON=0x70;   // x111 0000 - 8 Mhz internal clock 
 
 TRISC = 0x00;  // Set PORTC as Output 
 ANSEL = 0;     // Set as Digital I/O
 ANSELH = 0;    // Set as Digital I/O 
 PORTC = 0x00;  // All LEDs off
 
 TRISB  = 0xFF; // Set PORTB as Inputs
 
 // SSPCON = 0; // work around for PIC16F690 for revision A5 and previous
  
 //Configure as I2C slave
 //xxxx 0110 = I2C Slave mode, 7 bit address, no interrupts on start and stop
 //xxx1 xxxx = CKP = 1, Enable clock
 //xx1x xxxx = SSPEN, Enable SSP
 
 SSPCON = 0b00110110;

 SSPADD  = I2C_ADDR << 1; // Set I2C address 
 
 SSPSTAT = 0x00; // All bits must be cleared
 
 SSPIE = 1; // Enable the SSP module and the SSP interrupt
 SSPIF = 0;   
 PEIE = 1;
 GIE = 1;

 for(;;); // Do nothing...
}

void interrupt isr(void)           // Interrupt Service Routine
{if (SSPIF)                        // I2C interrupt
    {if(!DA && !RW && BF && START) // An address from master: write to slave 
      	{SSPBUF = SSPBUF;          // Empty buffer and clear BF bit	
		 if(SSPOV)                 // Check overflow
		    {//...                 // Overflow handling, if required
		     SSPOV = 0;
		    }
		 }
		    
	 else if(DA && !RW && BF)	// Data from master to slave  
	     {PORTC = SSPBUF;       // Output data to PORTC LEDs and clear BF bit	
		  if(SSPOV)             // Check overflow
		    {//...              // Overflow handling, if required   
		     SSPOV = 0;
		    }
		 }
	 else if(!DA && RW && !BF)	        // An address from master: read from slave	  
	     {SSPBUF = ++i2c_counter;       // Data will be write to master
    	  CKP = 1;                      // Release clock (data ready to be send to master)
		 }
	 else if(DA && RW && !BF && START)  // Read a byte from slave (next byte)
	 	 {SSPBUF = 255-i2c_counter;     // Data will be write to master
    	  CKP = 1;                      // Release clock (data ready to be send to master)
		 }
	 else if(DA && !RW && !BF)          // NAK from master (complete transmission has occurred)
	     {                           
		 }
	 	 
	}  
  SSPIF = 0;  // Re-enable interrupt
 }