Programming the Chip: Bootloaders and Programmers

How firmware gets into flash.

A hardware programmer talks to dedicated pins and writes your compiled program into flash. It can also set configuration bits such as clock source.

A bootloader is a small program already in flash that listens on a port such as UART at start-up and writes new firmware sent by your computer, so no programmer is needed.

Wrong configuration bits can lock you out, so read about them before changing anything.