Digital I/O

Pins as inputs and outputs: pinMode(), digitalWrite(), digitalRead() and the pin constants. More...

Functions
	pinMode (pin, mode)
	Sets a pin up as an input or an output.
	digitalWrite (pin, value)
	Sets an output pin high or low.
	digitalRead (pin)
	Reads a pin's level.

Variables
int	HIGH = 1
	Pin level: high (3.3 V).
int	LOW = 0
	Pin level: low (0 V).
int	INPUT = 0
	pinMode(): a digital input with no pull resistor.
int	OUTPUT = 1
	pinMode(): a digital output.
int	INPUT_PULLUP = 2
	pinMode(): a digital input pulled up to 3.3 V.
int	INPUT_PULLDOWN = 3
	pinMode(): a digital input pulled down to 0 V.
str	LED_BUILTIN = "LED"
	The on-board green LED.

Detailed Description

Pins as inputs and outputs: pinMode(), digitalWrite(), digitalRead() and the pin constants.

Function Documentation

pinMode()

pinMode	(		pin,
			mode )

Sets a pin up as an input or an output.

INPUT has no pull resistor, so an unconnected pin reads at random. For a button to 3.3 V use INPUT_PULLDOWN (pressed reads HIGH); for a button to GND use INPUT_PULLUP (pressed reads LOW). A0-A2 can be digital pins too. A pin on analogWrite() or tone() comes off PWM.

Parameters

pin	Pin number (2 is D2) or name ("D2", "A0", LED_BUILTIN).
mode	INPUT, OUTPUT, INPUT_PULLUP or INPUT_PULLDOWN.

Exceptions

ValueError

Unknown pin or mode, or an analogue-only pin (A3-A5).

Example

pinMode(2, INPUT_PULLUP)  # D2 reads HIGH until a button pulls it to GND
pinMode(LED_BUILTIN, OUTPUT)  # the LED's pin as an output

digitalWrite()

digitalWrite	(		pin,
			value )

Sets an output pin high or low.

A pin that is not an output yet (or is on analogWrite()) becomes one, so pinMode() is optional here. HIGH is 3.3 V; any true value counts as HIGH.

Parameters

pin	Pin number (2 is D2) or name ("D2", "A0", LED_BUILTIN).
value	HIGH or LOW.

Exceptions

ValueError

Unknown pin, or an analogue-only pin (A3-A5).

digitalRead()

digitalRead

(

pin

)

Reads a pin's level.

A pin that has not been set up with pinMode() becomes an INPUT, with no pull resistor; call pinMode() first for a button. An OUTPUT pin reads the level it is set to.

Parameters

pin	Pin number (2 is D2) or name ("D2", "A0").

Returns

HIGH or LOW.

Exceptions

ValueError

Unknown pin, or an analogue-only pin (A3-A5).