8 References
AVR151: Setup and Use of the SPI on megaAVR and tinyAVR:
http://www.atmel.com/images/atmel-2585-setup-and-use-of-the-spi_applicationnote_avr151.pdf
AVR311: Using the TWI Module as I2C Slave:
http://www.atmel.com/images/atmel-2565-using-the-twi-module-as-i2c-slave_applicationnote_avr311.pdf
AVR315: Using the TWI Module as I2C Master:
http://www.atmel.com/images/atmel-2564-using-the-twi-module-as-i2c-master_applicationnote_avr315.pdf
AVR319: Using the USI module for SPI communication:
http://www.atmel.com/images/doc2582.pdf
AVR1308: Using the XMEGA TWI:
http://www.atmel.com/images/doc8054.pdf
AVR1309: Using the XMEGA SPI:
http://www.atmel.com/images/doc8057.pdf
MSL2100 datasheet:
http://www.atmel.com/dyn/resources/prod_documents/F1_MSL2100_DB.pdf
MSL2160/61 datasheet:
http://www.atmel.com/dyn/resources/prod_documents/F1_MSL2160_DB.pdf
Atmel Studio 7: