Today, at the low end of the communication protocols we find the inter-integrated circuit (I 2 C) and the serial peripheral interface (SPI) protocols. Both protocols are well suited for communications between integrated circuits for slow communication with on-board peripherals. The two protocols coexist in modern digital electronics systems, and they probably will continue to compete in the future, as both I 2 C and SPI are actually quite complementary for this kind of communication.
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Frederic Leens (2009) studied this question.