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I'm designing a circuit with this LCD display. It will interface with STM32L0 MCU over SPI bus. as you can see, in LCD's datasheet there are only 3 lines of SPI pins. SCL - Clock, SI - Serial Data and CS.

I've wondered, is it because the LCD only receives data from SPI Master and not sending back any data? Is it possible to use SPI bus like that with route only 3 pins?

thank you!

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Is it possible to use SPI bus like that with route only 3 pins?

For sure. Many devices need only data from the master and do what they have to do without conferring with the master. I can think of DAC devices that produce an analogue output with just the data collected from the SPI bus. Some will communicate back to the master but only usually when setting up the registers of more complex devices; for a simple DAC, MISO is usually omitted: -

enter image description here

Digipots have a similar story; they mostly don't have MISO: -

enter image description here

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I've wondered, is it because the LCD only receives data from SPI Master and not sending back any data?

That is very well possible.

Is it possible to use SPI bus like that with route only 3 pins?

Yes, but floating pins are bad so add a pull-up to your MISO.

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