This application note describes a simple implementation of SD Card bootloader on ATxmega128A1U. The firmware runs on an XMEGA A1U Xplained Pro, connected by an I/O1 Xplained Pro holding a microSD card. The SD card is used as the SPI Slave and ATxmega128A1U acts as SPI Master. The binary file (test.bin) to be programmed is stored in the SD card. In Boot mode, the boot loader reads contents of the file and flashes image to the application section of the MCU flash memory.