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/************************************************************************* |
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* Title: I2C master library using hardware TWI interface |
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* Author: Peter Fleury <pfleury@gmx.ch> http://jump.to/fleury |
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* File: $Id: twimaster.c,v 1.3 2005/07/02 11:14:21 Peter Exp $ |
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* Software: AVR-GCC 3.4.3 / avr-libc 1.2.3 |
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* Target: any AVR device with hardware TWI |
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* Usage: API compatible with I2C Software Library i2cmaster.h |
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**************************************************************************/ |
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#include <inttypes.h> |
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#include <compat/twi.h> |
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#include <i2cmaster.h> |
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/* define CPU frequency in Mhz here if not defined in Makefile */ |
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#ifndef F_CPU |
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#define F_CPU 16000000UL |
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#endif |
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/* I2C clock in Hz */ |
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#define SCL_CLOCK 400000L |
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/************************************************************************* |
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Initialization of the I2C bus interface. Need to be called only once |
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*************************************************************************/ |
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void i2c_init(void) |
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{ |
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/* initialize TWI clock |
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* minimal values in Bit Rate Register (TWBR) and minimal Prescaler |
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* bits in the TWI Status Register should give us maximal possible |
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* I2C bus speed - about 444 kHz |
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* |
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* for more details, see 20.5.2 in ATmega16/32 secification |
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*/ |
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TWSR = 0; /* no prescaler */ |
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TWBR = 10; /* must be >= 10 for stable operation */ |
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}/* i2c_init */ |
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/************************************************************************* |
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Issues a start condition and sends address and transfer direction. |
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return 0 = device accessible, 1= failed to access device |
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*************************************************************************/ |
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unsigned char i2c_start(unsigned char address) |
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{ |
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uint8_t twst; |
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// send START condition |
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TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN); |
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// wait until transmission completed |
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while(!(TWCR & (1<<TWINT))); |
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// check value of TWI Status Register. Mask prescaler bits. |
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twst = TW_STATUS & 0xF8; |
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if ( (twst != TW_START) && (twst != TW_REP_START)) return 1; |
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// send device address |
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TWDR = address; |
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TWCR = (1<<TWINT) | (1<<TWEN); |
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// wail until transmission completed and ACK/NACK has been received |
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while(!(TWCR & (1<<TWINT))); |
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// check value of TWI Status Register. Mask prescaler bits. |
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twst = TW_STATUS & 0xF8; |
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if ( (twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK) ) return 1; |
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return 0; |
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}/* i2c_start */ |
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/************************************************************************* |
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Issues a start condition and sends address and transfer direction. |
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If device is busy, use ack polling to wait until device is ready |
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Input: address and transfer direction of I2C device |
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*************************************************************************/ |
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void i2c_start_wait(unsigned char address) |
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{ |
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uint8_t twst; |
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while ( 1 ) |
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{ |
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// send START condition |
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TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN); |
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// wait until transmission completed |
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while(!(TWCR & (1<<TWINT))); |
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// check value of TWI Status Register. Mask prescaler bits. |
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twst = TW_STATUS & 0xF8; |
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if ( (twst != TW_START) && (twst != TW_REP_START)) continue; |
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// send device address |
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TWDR = address; |
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TWCR = (1<<TWINT) | (1<<TWEN); |
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// wail until transmission completed |
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while(!(TWCR & (1<<TWINT))); |
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// check value of TWI Status Register. Mask prescaler bits. |
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twst = TW_STATUS & 0xF8; |
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if ( (twst == TW_MT_SLA_NACK )||(twst ==TW_MR_DATA_NACK) ) |
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{ |
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/* device busy, send stop condition to terminate write operation */ |
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TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO); |
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// wait until stop condition is executed and bus released |
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while(TWCR & (1<<TWSTO)); |
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continue; |
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} |
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//if( twst != TW_MT_SLA_ACK) return 1; |
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break; |
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} |
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}/* i2c_start_wait */ |
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/************************************************************************* |
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Issues a repeated start condition and sends address and transfer direction |
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Input: address and transfer direction of I2C device |
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Return: 0 device accessible |
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1 failed to access device |
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*************************************************************************/ |
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unsigned char i2c_rep_start(unsigned char address) |
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{ |
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return i2c_start( address ); |
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}/* i2c_rep_start */ |
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/************************************************************************* |
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Terminates the data transfer and releases the I2C bus |
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*************************************************************************/ |
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void i2c_stop(void) |
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{ |
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/* send stop condition */ |
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TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO); |
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// wait until stop condition is executed and bus released |
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while(TWCR & (1<<TWSTO)); |
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}/* i2c_stop */ |
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/************************************************************************* |
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Send one byte to I2C device |
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Input: byte to be transfered |
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Return: 0 write successful |
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1 write failed |
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*************************************************************************/ |
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unsigned char i2c_write( unsigned char data ) |
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{ |
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uint8_t twst; |
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// send data to the previously addressed device |
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TWDR = data; |
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TWCR = (1<<TWINT) | (1<<TWEN); |
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// wait until transmission completed |
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while(!(TWCR & (1<<TWINT))); |
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// check value of TWI Status Register. Mask prescaler bits |
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twst = TW_STATUS & 0xF8; |
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if( twst != TW_MT_DATA_ACK) return 1; |
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return 0; |
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}/* i2c_write */ |
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/************************************************************************* |
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Read one byte from the I2C device, request more data from device |
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Return: byte read from I2C device |
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*************************************************************************/ |
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unsigned char i2c_readAck(void) |
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{ |
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TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWEA); |
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while(!(TWCR & (1<<TWINT))); |
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return TWDR; |
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}/* i2c_readAck */ |
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/************************************************************************* |
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Read one byte from the I2C device, read is followed by a stop condition |
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Return: byte read from I2C device |
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*************************************************************************/ |
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unsigned char i2c_readNak(void) |
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{ |
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TWCR = (1<<TWINT) | (1<<TWEN); |
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while(!(TWCR & (1<<TWINT))); |
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return TWDR; |
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}/* i2c_readNak */ |