The interfaces available for the host communication may differ between end
applications. While the example bootloader is utilizing a basic configuration of the
UART to receive the application code, this can easily be updated as needed by replacing
the functions used as interface prototypes in boot.c.
/* Interface function prototypes */
#define BOOTLOADER_isRequested() BUTTON_read()
#define INTERFACE_init() USART_init()
#define INTERFACE_readByte() USART_read()
#define INTERFACE_writeByte(a) USART_write(a)
All AVR DA family have hardware UART, TWI, and SPI available for serial communication, and the I/O pins can also be used for custom digital protocols.