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
- /
- 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 16000000UL
- 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) && (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 */