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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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+
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+#include "twi.h"
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+
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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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+
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+/* I2C clock in Hz */
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+#define SCL_CLOCK 400000L
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+
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+
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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: 100 kHz clock, TWPS = 0 => prescaler = 1 */
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+
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+ TWSR = 0; /* no prescaler */
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+ TWBR = ((F_CPU/SCL_CLOCK)-16)/2; /* must be > 10 for stable operation */
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+
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+}/* i2c_init */
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+
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+
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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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+
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+ // send START condition
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+ TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
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+
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+ // wait until transmission completed
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+ while(!(TWCR & (1<<TWINT)));
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+
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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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+
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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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+
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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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+
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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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+
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+ return 0;
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+
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+}/* i2c_start */
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+
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+
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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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+
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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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+
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+
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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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+
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+ // wait until transmission completed
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+ while(!(TWCR & (1<<TWINT)));
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+
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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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+
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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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+
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+ // wail until transmission completed
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+ while(!(TWCR & (1<<TWINT)));
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+
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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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+
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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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+
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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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+
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+}/* i2c_start_wait */
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+
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+
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+/*************************************************************************
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+ Issues a repeated start condition and sends address and transfer direction
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+
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+ Input: address and transfer direction of I2C device
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+
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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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+
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+}/* i2c_rep_start */
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+
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+
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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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+
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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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+
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+}/* i2c_stop */
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+
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+
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+/*************************************************************************
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+ Send one byte to I2C device
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+
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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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+
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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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+
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+ // wait until transmission completed
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+ while(!(TWCR & (1<<TWINT)));
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+
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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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+
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+}/* i2c_write */
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+
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+
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+/*************************************************************************
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+ Read one byte from the I2C device, request more data from device
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+
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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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+
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+ return TWDR;
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+
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+}/* i2c_readAck */
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+
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+
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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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+
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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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+
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+ return TWDR;
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+
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+}/* i2c_readNak */
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