Keyestudio 4DOF - Digital I;O; TX and RX LED

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TX and RX LED
Onboard you can find two labels: RX(receive ) and TX (transmit)
First appear on digital pin 0 and 1 for serial communication;
Besides, the RX LED on the board will flash in different speed when serial data is being transmitted. The
flash speed depends on the baud rate set by board. And RX LED will also flash during the receiving
process.
Digital I/O
Arduino UNO has 14 digital input/output pins (of which 6 can be used as PWM outputs). These pins can
be configured as digital input pin to read the logic value (0 or 1). Or used as digital output pin to drive
different modules like LED, relay, etc. The pin labeled “〜” can be used to generate PWM.
AREF
Reference voltage( 0-5V) for the analog inputs. Used with analogReference().