Most standard SPLat boards designed from 2001 on (starting with the MMi99) will have two expansion connectors. These connectors will support two different sets of expansion connections:
The processor chips we use in SPLat have a lot of I/O pins, typically 40-50. Very many designs do not use up all these pins. By bringing unused pins out to the SPice connector, we make them available for expansion purposes, where they are used with what we term SPice boards.
What kind of pins are otherwise unused, and how many, will vary from one SPLat board to another. That is why there may be considerable difference between the SPice expansion capabilities of various SPLat boards, and why a SPice expansion board will generally only be suitable for hosting by one given SPLat controller board.
The SPx connector carries what is known as the SPI bus, plus some additional pins, and provides support for several diverse expansion schemes.
The SPI bus is an industry standard 3-wire high speed Serial Peripheral Interface. The processors we use in SPLat include built in SPI functionality.
SPI, in its native form, provides a rudimentary mechanism for shifting data in and out of a processor one byte at a time. On its own, SPI can provide basic I/O expansion with simple shift register chips. We use basic SPI in what we call SPiceX mode, where it allows modest expansion at very low cost. For the more advanced capabilities we use SPI plus a proprietary protocol, and call it SPx. At an intermediate level we use SPI, plus a strobe line, in XPice mode.
Virtually every future standard SPLat board will have the SPx connector.