SPI/I²C Bus Lines Control Multiple Peripherals

MAXIM

APPLICATION NOTE 4024
Jun 21, 2007

Abstract: This application note compares two common serial, digital interfaces used by most analog ICs: SPI™ or 3-wire, and I²C or 2-wire. Each serial interface offers advantages or disadvantages for many designs, depending on criteria such like needed data rate, space availability, and noise considerations. This application note discusses the differences between these two serial interfaces and presents examples to demonstrate each interface in detail.

Figure 1. Three-wire interfaces utilize data input, data output, clock, and chip-select lines.

Figure 3. Two-wire interfaces provide data input/output and clock lines.

Introduction Although real-world signals will always be analog, today more and more analog ICs communicate through digital interfaces. Serial interfaces communicate between a master, which provides the serial clock, and a slave/peripheral. Today's SPI (3-wire) and I²C (2-wire) ports found on most microcontrollers are popular means for transmitting and receiving data. Microcontrollers thus communicate over several bus lines to control peripherals including analog-to-digital converters (ADCs), digital-to-analog converters (DACs), smart batteries, port expanders, EEPROMs, and temperature sensors. Unlike data sent through a parallel interface, serial data is transmitted with numerous bits in succession, usually over two, three, or four data/timing lines. Although parallel interfaces offer speed, serial interfaces have the advantage of much fewer control and data lines.

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