Every expansion connector (on standard boards) will expose the SPI bus. The simplest way in which the SPI bus can be used is with a very simple I/O expansion system based on shift registers.

The SPI bus on the expansion connector can be used for shift register I/O expansion. This mode is referred to as SPiceX, because it is a simple scheme with limited capabilities, but very simple to implement.

Programming of SPiceX is achieved by a simple adaption of the SPx programming model described later. In its unadorned form it will require a fairly sophisticated programmer to handle it. Tutorial

SPiceX is best suited to providing fairly large amounts of digital I/O. It is well suited to solutions based around available SPI-compatible chips, for example multi-segment LED drivers. It has the advantage of very simple hardware, but on the downside it will not provide on-screen simulation of those I/Os, and programming will be less convenient than the basic built in I/O.

There is no reason why we can’t make expansion boards that combine SPice and SPiceX. Usually there can only be one SPice/SPiceX board connected to a SPLat.