is there any easy to understand and use way to use an arduino uno as an spi slave? i need this knowledge for a project.
or if you want and have the skill make a library that i can download to make it easier. remember to tell me how it works.

Look here, it’s a good start :slight_smile:

that comes from Gammon Forum : Electronics : Microprocessors : SPI - Serial Peripheral Interface - for Arduino

Nick Gammon full tutorial on SPI including slave mode and code.

The section that you want most is "How to make an SPI slave" but the rest of the info on how SPI works might come in handy.