SPI

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Last Updated: Thursday, 28 August 2025 23:21

Published: Saturday, 30 October 2021 06:39

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SPI and QSPI

SPI = Serial Peripheral interface. It is very popular 4 wire interface, and is supported in many tiny chips because of it's simplicity.

SPI has a master and slave. 

Master drives these 3 pins:

• CLK
• MOSI (Dataout pin) along with 
• CSn (Chip Select pin) to select slave. We can multiple of these and pull only one of them low to have that particular slave drive the MISO pin (see below)

Slave drives this 1 pin:

• MISO (Datain pin)

Wikipedia article with basics: https://en.wikipedia.org/wiki/Serial_Peripheral_Interface

SPI timing diagram with waveform => spi_diagram.jpg

QSPI: Quad SPI

A very good tutorial here: https://embeddedinventor.com/quad-spi-everything-you-need-to-know/