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The startup logic for the A-Star 32U4 bootloader.
Brown-out detection
Unlike many other ATmega32U4 boards, the A-Stars have brown-out detection enabled. The brown-out
threshold is 4.3 V, and if the voltage on VCC goes below this then the AVR will reset. The bootloader was
designed so that the user program can detect brown-out resets. To do so, check to see if the BORF bit in the
Pololu Zumo 32U4 Robot User’s Guide
© 2001–2015 Pololu Corporation
8. The A-Star 32U4 Bootloader
Page 71 of 76