1. What is this library?
2. Contents of this library
3. Supported devices
4. Functions in this library

This library is an I2C master library which uses the TWI peripheral inside the AVR microcontroller to establish connections using the I2C protocol

The library contains the following files:

• main.c
• I2C_master.c
• I2C_master.h

This is a piece of example code which uses this library to read out and HMC5338L digital compass sensor.

This file contains all the function declarations to setup and work with the TWI hardware peripheral inside the AVR.

Make sure you add this source file to your Makefile!

This file contains the function prototypes and the definition of the Read / Write bit (0 = read, 1 = write)

This file has to be included in your source file

Though I have only tested this library on an ATmega328P it should be running on all major ATmega AVRs like:

• ATmega644
• ATmega32
• ATmega16
• ATmega328/P
• ATmega168/P
• ATmega88/P
• ATmega44/P
• ATmega8

If your device is not supported you can probably adapt this library easily to your needs by having a look at the your device's datasheet and changing the register names appropriately

The ATtiny range of microcontrolles is not supported as they only provide a USI peripheral which is completely different from the TWI peripheral used on the other controllers

• void I2C_init(void)
• uint8_t I2C_start(uint8_t address)
• uint8_t I2C_write(uint8_t data)
• uint8_t I2C_read_ack(void)
• uint8_t I2C_read_nack(void);
• void I2C_stop(void)

This function needs to be called only once to set up the correct SCL frequency for the bus

This function needs to be called any time a connection to a new slave device should be established. The function returns 1 if an error has occured, otherwise it returns 0.

The syntax to start a operation write to a device is either: I2C_start(SLAVE_ADDRESS+I2C_WRITE); or I2C_start(SLAVE_WRITE_ADDRESS);

The syntax to start a read operation from a device is either: I2C_start(SLAVE_ADDRESS+I2C_READ); or I2C_start(SLAVE_READ_ADDRESS);

This function is used to write data to the currently active device. The only parameter this funcion takes is the 8 bit unsigned integer to be sent. The function returns 1 if an error has occured, otherwise it returns 0.

This function is used to read one byte from a device and request another byte of data after the transmission is complete by sending the acknowledge bit. This function returns the received byte.

This function is used to read one byte from a device an then not requesting another byte and therefore stoping the current transmission. This function returns the received byte.

This function disables the TWI peripheral completely and therefore disconnects the device from the bus