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+#+TITLE:  SPI for microprocessors
+#+SETUPFILE: ../../options.org
+
+Bremen, Germany, {{{date}}}
+
+SPI is a useful serial communications interface. It is used in
+hobbyist projects to control from memory ICs to LCD screens and it's
+even possible to read SD cards through it.
+
+Most modern microcontrollers are equiped with built-in SPI support,
+which can be easily used from code without much hardware required. But
+what happends when one wants to interface SPI peripherals with old
+microprocessors? These usually don't have any built-in peripherals and
+, as far as I am aware, there are no enternal peripherals one can buy.
+
+This article aims to provide an overview of how SPI works, the
+instructions on how to build a SPI module for old microprocessors like
+the Z80 and the explanation of how such a module operates.
+
+This is also a part of my ongoing series on the progress of my [[local:/z80][Z80
+based project]].
+
+** Table of Contents
+1) [[#how-does-spi-work][How does SPI work]]
+
+#+NAME: how-does-spi-work
+** 1. How does SPI work
+:PROPERTIES:
+:CUSTOM_ID: how-does-spi-work
+:END: