1) On-board LED
Each Arduino has an on-board LED connected to one of its pins. HITIPanel indicates which one it is with a dot. On most boards (Uno, Mega, Nano, Leonardo, Micro), it is pin 13. On MKR boards, it is pin 6.
HITIPanel indicates when hardware serial communication is activated on a pin.
HITIPanel indicates when TWI / I2C is activated on a pin.
HITIPanel indicates when SPI is activated on a pin.