De facto industry convention (originated at Motorola; no single ratifying body)
SPI (Serial Peripheral Interface) is maintained by De facto industry convention (originated at Motorola; no single ratifying body). The current version is No formal version — vendor application notes only. The register lists it as active. The specification is openly available.
A four-wire, full-duplex bus for connecting a host to one or more peripherals at much higher speed than I²C, at the cost of needing a dedicated chip-select line per device. No single body ever formally standardized SPI — it spread as a de facto convention from Motorola's original microcontroller documentation, and every vendor's implementation is technically a variant.
The full reference entry is for registered members. Registration is free and takes a minute. You come back to this page afterwards.