The SPI bus
The Serial Peripheral Interface (SPI) protocol implements a synchronous serial link between a master and a slave. When a single slave is used, only three signals (and ground) are needed.
The master generates an SCLK (serial clock) clock signal, which is sent to the slave. On some transitions of this clock, the slave will read data using the appointed signal, MOSI (short for master out, slave in), or write it using the signal named MISO (master in, slave out). There are several names, depending on hardware manufacturers, used to describe these signals. It is recommended to use the MISO/MOSI notation (the most common one), because it removes any ambiguity: the MOSI pin of a master must always be connected to the MOSI pin of a slave, and the same is true for the MISO pin.
If several slaves are to be connected to the same host, they may be connected in parallel (all MISO pins connected together as well as all MOSI pins), but an additional signal (CS, or Chip Select) is required for...
