The Synchronous Peripheral Interface (SPI) standard is gaining rapidly in popularity.It allows faster communication than I2C and can be implemented usingfewer gates which means lower silicon costs. Although the larger AVR family members include a fully-functional SPI interface, the smaller members do not.This application note describes a set of low-level routines for software implementation of the SPI protocol, in Master Mode (all communications originate from the AVR). These can be used as the basis for communicating with Atmel’s 25XXX family of serial EEPROM memories,as well as a host of other peripheral IC’s such as display drivers.