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Twimaster.c

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<source lang="c"> /*************************************************************************

  • Title: I2C master library using hardware TWI interface
  • Author: Peter Fleury <pfleury@gmx.ch> http://jump.to/fleury
  • File: $Id: twimaster.c,v 1.3 2005/07/02 11:14:21 Peter Exp $
  • Software: AVR-GCC 3.4.3 / avr-libc 1.2.3
  • Target: any AVR device with hardware TWI
  • Usage: API compatible with I2C Software Library i2cmaster.h
                                                                                                                                                    • /
  1. include <inttypes.h>
  2. include <compat/twi.h>
  1. include "i2cmaster.h"


/* define CPU frequency in Mhz here if not defined in Makefile */

  1. ifndef F_CPU
  2. define F_CPU 16000000UL
  3. endif

/* I2C clock in Hz */

  1. 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 = ((F_CPU/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 */