As stated in the SPI documentation page, the SPI library can only be used for the Arduino in Master mode. You can use the constants and such from the library but you have to do transmissions manually if you want to use it in Slave mode.
As stated in the SPI documentation page, the SPI library can only be used for the Arduino in Master mode. You can use the constants and such from the library but you have to do transmissions manually if you want to use it in Slave mode.