EIA JESD 251:2018

This standard specifies the eXpanded Serial Peripheral Interface (xSPI) for Non Volatile Memory Devices, which provides high data throughput, low signal count, and limited backward compatibility with legacy Serial Peripheral Interface (SPI) devices. It is primarily for use in computing, automotive, Internet Of Things (IOT), embedded systems and mobile systems, between host processing and peripheral devices. The xSPI electrical interface can deliver up to 400 MBytes per second raw data throughput.