//**************************************************************
//    ******** FUNCTIONS FOR I2C COMMUNICATION  *******
//**************************************************************
//Controller:	ATmega128 (Crystal: 16Mhz)
//Compiler:		winAVR (AVR-GCC)
//Author:		CC Dharmani, Chennai (India)
//				www.dharmanitech.com
//Date:			April 2009
//********************************************************

//link to post: http://www.dharmanitech.com/2008/08/interfacing-rtc-serial-eeprom-using-i2c.html


#include <avr/io.h>
#include "i2c_routines.h"
#include "UART_routines.h"

//*************************************************
//Function to start i2c communication
//*************************************************
unsigned char i2c_start(void)
{
 
	TWCR = (1<<TWINT)|(1<<TWSTA)|(1<<TWEN); 	//Send START condition
	
    while (!(TWCR & (1<<TWINT)));   		//Wait for TWINT flag set. This indicates that the
		  								//START condition has been transmitted
    if ((TWSR & 0xF8) == START)			//Check value of TWI Status Register
 	   return(0);
	else
	   return(1);
}

//*************************************************
//Function for repeat start condition
//*************************************************
unsigned char i2c_repeatStart(void)
{
 
    TWCR = (1<<TWINT)|(1<<TWSTA)|(1<<TWEN); 		//Send START condition
    while (!(TWCR & (1<<TWINT)));   		//Wait for TWINT flag set. This indicates that the
		  								//START condition has been transmitted
    if ((TWSR & 0xF8) == REPEAT_START)			//Check value of TWI Status Register
 	   return(0);
	else
	   return(1);
}
//**************************************************
//Function to transmit address of the slave
//*************************************************
unsigned char i2c_sendAddress(unsigned char address)
{
   unsigned char STATUS;
   
   if((address & 0x01) == 0) 
     STATUS = MT_SLA_ACK;
   else
     STATUS = MR_SLA_ACK; 
   
   TWDR = address; 
   TWCR = (1<<TWINT)|(1<<TWEN);	   //Load SLA_W into TWDR Register. Clear TWINT bit
   		  			 				   //in TWCR to start transmission of address
   while (!(TWCR & (1<<TWINT)));	   //Wait for TWINT flag set. This indicates that the
   		 		   					   //SLA+W has been transmitted, and
									   //ACK/NACK has been received.
   if ((TWSR & 0xF8) == STATUS)	   //Check value of TWI Status Register
   	  return(0);
   else 
      return(1);
}

//**************************************************
//Function to transmit a data byte
//*************************************************
unsigned char i2c_sendData(unsigned char data)
{
   TWDR = data; 
   TWCR = (1<<TWINT) |(1<<TWEN);	   //Load SLA_W into TWDR Register. Clear TWINT bit
   		  			 				   //in TWCR to start transmission of data
   while (!(TWCR & (1<<TWINT)));	   //Wait for TWINT flag set. This indicates that the
   		 		   					   //data has been transmitted, and
									   //ACK/NACK has been received.
   if ((TWSR & 0xF8) != MT_DATA_ACK)   //Check value of TWI Status Register
   	  return(1);
   else
      return(0);
}

//*****************************************************
//Function to receive a data byte and send ACKnowledge
//*****************************************************
unsigned char i2c_receiveData_ACK(void)
{
  unsigned char data;
  
  TWCR = (1<<TWEA)|(1<<TWINT)|(1<<TWEN);
  
  while (!(TWCR & (1<<TWINT)));	   	   //Wait for TWINT flag set. This indicates that the
   		 		   					   //data has been received
  if ((TWSR & 0xF8) != MR_DATA_ACK)    //Check value of TWI Status Register
   	  return(ERROR_CODE);
  
  data = TWDR;
  return(data);
}

//******************************************************************
//Function to receive the last data byte (no acknowledge from master
//******************************************************************
unsigned char i2c_receiveData_NACK(void)
{
  unsigned char data;
  
  TWCR = (1<<TWINT)|(1<<TWEN);
  
  while (!(TWCR & (1<<TWINT)));	   	   //Wait for TWINT flag set. This indicates that the
   		 		   					   //data has been received
  if ((TWSR & 0xF8) != MR_DATA_NACK)    //Check value of TWI Status Register
   	  return(ERROR_CODE);
  
  data = TWDR;
  return(data);
}
//**************************************************
//Function to end the i2c communication
//*************************************************   	
void i2c_stop(void)
{
  TWCR =  (1<<TWINT)|(1<<TWEN)|(1<<TWSTO);	  //Transmit STOP condition
}