Author: Kerry Scharfglass / Source: Hackaday
Interfacing with the outside world is a fairly common microcontroller task. Outside of certain use cases microcontrollers are arguably primarily useful because of how easily they can interface with other devices. If we just wanted to read and write some data we wouldn’t have gotten that Arduino!
But some tasks are more common than others; for instance we’re used to being on the master side of the interface equation, not the slave side. (That’s the job for the TI engineer who designed the temperature sensor, right?) As [Pat] discovered when mocking out a missing SPI GPIO extender, sometimes playing the other role can contain unexpected difficulties.The simple case for a SPI slave is exactly that: simple. SPI can be wonderful in its apparent simplicity. Unlike I2C there are no weird addressing schemes, read/write bits, stop and start clock conditions. You toggle a clock line and a bit of data comes out, as long as you have the right polarity schemes of course. As a slave device the basic algorithm is of commensurate complexity. Setup…
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