https://github.com/MicrochipTech/avr_insights Do you want to connect a microcontroller to an SD card? Learn the basics of Serial Peripheral Interface (SPI) protocol on AVR devices in this introduction video. This will enable your AVR microcontroller to communicate with multiple other devices at the same time! Use the SPI bus to communicate between a master device and one or multiple slave devices with AVR microcontrollers. SPI uses MISO and MOSI lines to communicate between devices, the SCK or clock line to maintain a consistent clock between devices, and a SS or Slave Select line to pick which peripheral device is communicating with the master device. Documentation references -------------------------------------------------------------- Atmel Tools Documentation: https://mchp.us/2Vz6gEJ AVR Libc reference manual: https://mchp.us/2W4g9cI ATmega324PB datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/40001908A.pdf#page=230 ATmega 324PB Xplained Pro User Guide: http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-42633-ATmega324PB-Xplained-Pro_User-Guide.pdf App note AVR319: http://ww1.microchip.com/downloads/en/AppNotes/Atmel-2582-Using-the-USI-Module-for-SPI-Communication-on-tinyAVR-and-megaAVR-Devices_ApplicationNote_AVR319.pdf