C Code for Interfacing I2C module in AVR MCU

[Magneto]

i2cmaster.h Header File

#ifndef _I2CMASTER_H
#define _I2CMASTER_H 1
/*************************************************************************
* Title: C include file for the I2C master interface
* (i2cmaster.S or twimaster.c)
* Software: AVR-GCC 3.4.3 / avr-libc 1.2.3
* Target: any AVR device
* Usage: see Doxygen manual
**************************************************************************/

#ifdef DOXYGEN
/**
@defgroup pfleury_ic2master I2C Master library
@code #include <i2cmaster.h> @endcode

@brief I2C (TWI) Master Software Library

Basic routines for communicating with I2C slave devices. This single master
implementation is limited to one bus master on the I2C bus.

This I2c library is implemented as a compact assembler software implementation of the I2C protocol
which runs on any AVR (i2cmaster.S) and as a TWI hardware interface for all AVR with built-in TWI hardware (twimaster.c).
Since the API for these two implementations is exactly the same, an application can be linked either against the
software I2C implementation or the hardware I2C implementation.

Use 4.7k pull-up resistor on the SDA and SCL pin.

Adapt the SCL and SDA port and pin definitions and eventually the delay routine in the module
i2cmaster.S to your target when using the software I2C implementation !

Adjust the CPU clock frequence F_CPU in twimaster.c or in the Makfile when using the TWI hardware implementaion.

@note
The module i2cmaster.S is based on the Atmel Application Note AVR300, corrected and adapted
to GNU assembler and AVR-GCC C call interface.
Replaced the incorrect quarter period delays found in AVR300 with
half period delays.

@author Peter Fleury [email protected] http://jump.to/fleury

@par API Usage Example
The following code shows typical usage of this library, see example test_i2cmaster.c

@code

#include <i2cmaster.h>


#define Dev24C02 0xA2 // device address of EEPROM 24C02, see datasheet

int main(void)
{
unsigned char ret;

i2c_init(); // initialize I2C library

// write 0x75 to EEPROM address 5 (Byte Write)
i2c_start_wait(Dev24C02+I2C_WRITE); // set device address and write mode
i2c_write(0x05); // write address = 5
i2c_write(0x75); // write value 0x75 to EEPROM
i2c_stop(); // set stop conditon = release bus


// read previously written value back from EEPROM address 5
i2c_start_wait(Dev24C02+I2C_WRITE); // set device address and write mode

i2c_write(0x05); // write address = 5
i2c_rep_start(Dev24C02+I2C_READ); // set device address and read mode

ret = i2c_readNak(); // read one byte from EEPROM
i2c_stop();

for(;;);
}
@endcode

*/
#endif /* DOXYGEN */

/**@{*/

#if (__GNUC__ * 100 + __GNUC_MINOR__) < 304
#error "This library requires AVR-GCC 3.4 or later, update to newer AVR-GCC compiler !"
#endif

#include <avr/io.h>

/** 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


/**
@brief initialize the I2C master interace. Need to be called only once
@param void
@return none
*/
extern void i2c_init(void);


/**
@brief Terminates the data transfer and releases the I2C bus
@param void
@return none
*/
extern void i2c_stop(void);


/**
@brief Issues a start condition and sends address and transfer direction

@param addr address and transfer direction of I2C device
@retval 0 device accessible
@retval 1 failed to access device
*/
extern unsigned char i2c_start(unsigned char addr);


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

@param addr address and transfer direction of I2C device
@retval 0 device accessible
@retval 1 failed to access device
*/
extern unsigned char i2c_rep_start(unsigned char addr);


/**
@brief Issues a start condition and sends address and transfer direction

If device is busy, use ack polling to wait until device ready
@param addr address and transfer direction of I2C device
@return none
*/
extern void i2c_start_wait(unsigned char addr);


/**
@brief Send one byte to I2C device
@param data byte to be transfered
@retval 0 write successful
@retval 1 write failed
*/
extern unsigned char i2c_write(unsigned char data);


/**
@brief read one byte from the I2C device, request more data from device
@return byte read from I2C device
*/
extern unsigned char i2c_readAck(void);

/**
@brief read one byte from the I2C device, read is followed by a stop condition
@return byte read from I2C device
*/
extern unsigned char i2c_readNak(void);

/**
@brief read one byte from the I2C device

Implemented as a macro, which calls either i2c_readAck or i2c_readNak

@param ack 1 send ack, request more data from device<br>
0 send nak, read is followed by a stop condition
@return byte read from I2C device
*/
extern unsigned char i2c_read(unsigned char ack);
#define i2c_read(ack) (ack) ? i2c_readAck() : i2c_readNak();


/**@}*/
#endif


twimaster.c File

/*************************************************************************
* Title: I2C master library using hardware TWI interface
* 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
**************************************************************************/
#include <inttypes.h>
#include <compat/twi.h>

#include <i2cmaster.h>


/* define CPU frequency in Mhz here if not defined in Makefile */
#ifndef F_CPU
#define F_CPU 4000000UL
#endif

/* 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 = ((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) 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 */