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+#ifndef _I2CMASTER_H
+#define _I2CMASTER_H   1
+/************************************************************************* 
+* Title:    C include file for the I2C master interface 
+*           (i2cmaster.S or twimaster.c)
+* Author:   Peter Fleury <pfleury@gmx.ch>  http://jump.to/fleury
+* File:     $Id: i2cmaster.h,v 1.10 2005/03/06 22:39:57 Peter Exp $
+* 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 pfleury@gmx.ch  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