Pololu A-Star 32U4 - Manual (Page 26)

pinMode(13, OUTPUT);
if (MCUSR & (1 << BORF))
{
// A brownout reset occurred. Blink the LED
// quickly for 2 seconds.
for(uint8_t i = 0; i < 10; i++)
{
digitalWrite(13, HIGH);
delay(100);
digitalWrite(13, LOW);
delay(100);
}
}
MCUSR = 0;
Pololu A-Star 32U4 User’s Guide © 2001–2014 Pololu Corporation
7. The A-Star 32U4 Bootloader Page 26 of 30