4.2 Interfaces

The interfaces available for the host communication may differ between end applications. While the example bootloader is utilizing a basic configuration of the USART peripheral to receive the application code, this can easily be updated as needed, by replacing the three UART functions in boot.c:

‘static void init_uart(void)’
‘static uint8_t uart_receive(void)’
‘static void uart_send(uint8_t byte)’

All tinyAVR^® 0- and 1-series, and megaAVR^® 0-series devices have hardware USART, TWI and SPI peripherals available for serial communication, and the I/O pins can also be used for custom digital protocols.

The available peripheral interrupts can be used in the bootloader code by relocating the interrupt vector table to the start of boot section. This is done by enabling the IVSEL bit in the CPUINT.CTRLA register. For more information, see AN1982 - Interrupt System in tinyAVR 0- and 1-series, and megaAVR 0-series.

A bootloader code example using the TWI peripheral in Slave mode is also available. It it located in a .zip file related to this application note.