AVRFreaks.net

#include <avr/io.h>
#include <util/delay.h>
#include <stdlib.h>
#include <avr/interrupt.h>
#include <compat/twi.h>

#define TC74  0b1001101      // device address of TC74


/*uC Clock*/
#define uC_Clock 8000000L


/** defines the data direction (reading from I2C device) in i2c_start(),i2c_rep_start() */
#define I2C_READ    1

/** defines the data direction (writing to I2C device) in i2c_start(),i2c_rep_start() */
#define I2C_WRITE   0

/* I2C clock in Hz */
#define SCL_CLOCK  100000L


/*************************************************************************
 Initialization of the I2C bus interface. Need to be called only once
*************************************************************************/
void i2c_init(void)
{
  /* initialize TWI clock: 100 kHz clock, TWPS = 0 => prescaler = 1 */
 
  TWSR = 0;                         /* no prescaler */
  TWBR = ((uC_Clock/SCL_CLOCK)-16)/2;  /* must be > 10 for stable operation */

}/* i2c_init */


/*************************************************************************   
  Issues a start condition and sends address and transfer direction.
  return 0 = device accessible, 1= failed to access device
*************************************************************************/
unsigned char i2c_start(unsigned char address)
{
    uint8_t   twst;

   // send START condition
   TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);

   // wait until transmission completed
   while(!(TWCR & (1<<TWINT)));

   // check value of TWI Status Register. Mask prescaler bits.
   twst = TW_STATUS & 0xF8;
   if ( (twst != TW_START) && (twst != TW_REP_START)) return 1;

   // send device address
   TWDR = address;
   TWCR = (1<<TWINT) | (1<<TWEN);

   // wail until transmission completed and ACK/NACK has been received
   while(!(TWCR & (1<<TWINT)));

   // check value of TWI Status Register. Mask prescaler bits.
   twst = TW_STATUS & 0xF8;
   if ( (twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK) ) return 1;

   return 0;

}/* i2c_start */


/*************************************************************************
 Issues a start condition and sends address and transfer direction.
 If device is busy, use ack polling to wait until device is ready
 
 Input:   address and transfer direction of I2C device
*************************************************************************/
void i2c_start_wait(unsigned char address)
{
    uint8_t   twst;


    while ( 1 )
    {
       // send START condition
       TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
   
       // wait until transmission completed
       while(!(TWCR & (1<<TWINT)));
   
       // check value of TWI Status Register. Mask prescaler bits.
       twst = TW_STATUS & 0xF8;
       if ( (twst != TW_START) && (twst != TW_REP_START)) continue;
   
       // send device address
       TWDR = address;
       TWCR = (1<<TWINT) | (1<<TWEN);
   
       // wail until transmission completed
       while(!(TWCR & (1<<TWINT)));
   
       // check value of TWI Status Register. Mask prescaler bits.
       twst = TW_STATUS & 0xF8;
       if ( (twst == TW_MT_SLA_NACK )||(twst ==TW_MR_DATA_NACK) )
       {          
           /* device busy, send stop condition to terminate write operation */
           TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
          
           // wait until stop condition is executed and bus released
           while(TWCR & (1<<TWSTO));
          
           continue;
       }
       //if( twst != TW_MT_SLA_ACK) return 1;
       break;
     }

}/* i2c_start_wait */


/*************************************************************************
 Issues a repeated start condition and sends address and transfer direction

 Input:   address and transfer direction of I2C device
 
 Return:  0 device accessible
          1 failed to access device
*************************************************************************/
unsigned char i2c_rep_start(unsigned char address)
{
    return i2c_start( address );

}/* i2c_rep_start */


/*************************************************************************
 Terminates the data transfer and releases the I2C bus
*************************************************************************/
void i2c_stop(void)
{
    /* send stop condition */
   TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
   
   // wait until stop condition is executed and bus released
   while(TWCR & (1<<TWSTO));

}/* i2c_stop */


/*************************************************************************
  Send one byte to I2C device
 
  Input:    byte to be transfered
  Return:   0 write successful
            1 write failed
*************************************************************************/
unsigned char i2c_write( unsigned char data )
{   
    uint8_t   twst;
   
   // send data to the previously addressed device
   TWDR = data;
   TWCR = (1<<TWINT) | (1<<TWEN);

   // wait until transmission completed
   while(!(TWCR & (1<<TWINT)));

   // check value of TWI Status Register. Mask prescaler bits
   twst = TW_STATUS & 0xF8;
   if( twst != TW_MT_DATA_ACK) return 1;
   return 0;

}/* i2c_write */


/*************************************************************************
 Read one byte from the I2C device, request more data from device
 
 Return:  byte read from I2C device
*************************************************************************/
unsigned char i2c_readAck(void)
{
   TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWEA);
   while(!(TWCR & (1<<TWINT)));   

    return TWDR;

}/* i2c_readAck */


/*************************************************************************
 Read one byte from the I2C device, read is followed by a stop condition
 
 Return:  byte read from I2C device
*************************************************************************/
unsigned char i2c_readNak(void)
{
   TWCR = (1<<TWINT) | (1<<TWEN);
   while(!(TWCR & (1<<TWINT)));
   
    return TWDR;

}/* i2c_readNak */


int main(void)
{
    unsigned char ret;

    DDRB  = 0xff;               // use all pins on port B for output
    PORTB = 0xff;               // (active low LED's )

   _delay_ms(1000);

    i2c_init();                 // init I2C interface
   
    i2c_start(0x9A);             // set device address and write mode
      
   
   i2c_write(0x00);
   
   i2c_rep_start(0x9B);       // set device address and read mode
   
   PORTB = i2c_readNak();
   
   i2c_stop();
   
   
   
   for(;;)
   {
   
   i2c_start(0x9A);       // set device address and write mode
      
   
   i2c_write(0x00);
   
   i2c_rep_start(0x9B);       // set device address and read mode
   
   PORTB = i2c_readNak();      //Temperature can be read on PORTB pins
   
   i2c_stop();
   
   _delay_ms(1000);
   
   
   }

}

i2c_start(TC74+I2C_WRITE);