I2C fundamental

I²C( read as I square C) bus first introduced by Philips. Because of its simplicity and flexibility the I²C bus has become one of the most microcontroller bus system used for interfacing various IC. The I²C bus use only 2 bidirectional data lines for communicating with the microcontroller and the I²C protocol specification can support up to 128(27-1) devices attached to the bus.
The I²C protocol use master and slave method, the master which is usually the microcontroller which the slave can be any I²C devices such as serial EEPROM, I/O Expender or even another microcontroller. As the name I²C use only 2 pin to control up to 127 devices.

The 2 controlling pin are –

SDA: Serial Data pin.

SCL: Serial Clock (Synchronize clock)

Each slave devices have their own individual 7 bits of address length

Bit0 represent R/W, For Read bit0= 1 and Write bit0 = 0.

Let’s look at the bits available in AVR family-

Let’s make the user defined function of start, transmission and stop condition.

uint8_t I2C_Start(void) -> TWI start or repeat start

uint8_t I2C_Start(void)
{
	TWCR=(1<<TWEN)|(1<<TWINT)|(1<<TWSTA); //--- TWI Interrupt disable, TWI enable, TWI Start
	while(!(TWCR&(1<<TWINT)));           //--- Wait until start condition is executed
	return(TWSR&0xF8);
}

void I2C_Stop(void) -> TWI stop condition

void I2C_Stop(void)	
{
    TWCR=(1<<TWSTO)|(1<<TWINT)|(1<<TWEN);//--- TWI Interrupt disable, TWI enable, TWI Stop
    while(TWCR&(1<<TWSTO));	              //--- Wait until stop condition execution
}

uint8_t I2C_Write(char data) -> TWI write condition

uint8_t I2C_Write(char data)
{
	TWDR=data;
	TWCR=(1<<TWEN)|(1<<TWINT);            //--- TWI Interrupt disable, TWI enable
	while(!(TWCR&(1<<TWINT)));            //--- Wait until start condition is executed
	return(TWSR&0xF8);
}

Read function can be done with Acknowledge or without Acknowledge.

char I2C_Read_Ack(void) -> Read with Acknowledge

char I2C_Read_Ack(void)	
{
    TWCR=(1<<TWEN)|(1<<TWINT)|(1<<TWEA); //--- TWI Interrupt disable, TWI enable, TWI Accknowledge
    while(!(TWCR&(1<<TWINT)));           //--- Wait until transmit is complete
    return TWDR;			             //--- Return received data
}

char I2C_Read_Nack(void) -> Read without Acknowledge

char I2C_Read_Nack(void)		
{
    TWCR=(1<<TWEN)|(1<<TWINT);	//--- TWI Interrupt disable, TWI enable
    while(!(TWCR&(1<<TWINT)));	//--- Wait until transmit is complete
    return TWDR;		        //--- Return received data
}

Those functions are used according to datasheet provided by the IC. We will Interface I²C in the next article.