The Serial Peripheral Interface or SPI-bus is a simple 4- wire serial communications interface used by many peripheral chips that enable the controllers (SoCs’ and Microcontrollers/Microprocessors) and peripheral devices to communicate with each other. The Dual/Quad SPI is an enhancement to the Standard SPI protocol (described in the Motorola M68HC11 datasheet) and provides a simple method for data exchange between a master and a slave.