Using SPI to control an LED matrix

In Chapter 10, Sensing and Displaying Real-World Data, we connected to devices using a bus protocol called I²C. Raspberry Pi also supports another chip-to-chip protocol called Serial Peripheral Interface (SPI). The SPI bus differs from I²C because it uses two single direction data lines (where I²C uses one bidirectional data line).

Although SPI requires more wires (I²C uses two bus signals, SDA and SCL), it supports the simultaneous sending and receiving of data and much higher clock speeds than I²C:

General connections of SPI devices with Raspberry Pi

The SPI bus consists of the following four signals:

• SCLK: This allows the clock edges to read/write data on the input/output lines; it is driven by the master device. As the clock signal changes from one state to another, the SPI device will check the state of the MOSI signal to read a single bit. Similarly, if the SPI device is sending data, it will use the clock signal edges to synchronize when it sets the...