Particle

Input/Output

digitalRead()

Reads the value from a specified digital pin, either HIGH or LOW.

// PROTOTYPE
int32_t digitalRead(uint16_t pin)

digitalRead() takes one argument, pin: the number of the digital pin you want to read.

digitalRead() returns HIGH or LOW.

// EXAMPLE USAGE
int button = D0;                   // button is connected to D0
int LED = D1;                      // LED is connected to D1
int val = 0;                       // variable to store the read value

void setup()
{
  pinMode(LED, OUTPUT);            // sets pin as output
  pinMode(button, INPUT_PULLDOWN); // sets pin as input
}

void loop()
{
  val = digitalRead(button);       // read the input pin
  digitalWrite(LED, val);          // sets the LED to the button's value
}

Gen 3 Devices (B Series SoM, Tracker SoM, Tracker One, Boron, Argon, and E404X):

For all Feather Gen 3 devices (Argon, Boron, Xenon) all GPIO pins (A0..A5, D0..D13) can be used for digital input as long they are not used otherwise (e.g. as Serial1 RX/TX).
For the Boron SoM all GPIO pins (A0..A7, D0..D13, D22, D23) can be used for digital input as long they are not used otherwise (e.g. as Serial1 RX/TX).
For the Tracker SoM all GPIO pins (A0..A7, D0..D9) can be used for digital input as long they are not used otherwise (e.g. as Serial1 RX/TX). Note that on the Tracker SoM pins A0 - A7 and the same physical pins as D0 - D7 and are just alternate names for the same pins.
GPIO are not 5V tolerant on Gen 3 devices. Be sure the input voltage does not exceed 3.3V (typical) or 3.6V (absolute maximum).

P2 and Photon 2 Devices:

All GPIO pins (A0, A1, A2, A5, D0..D10, MOSI, MISO, SCK, RX, TX) can be used as long they are not used otherwise (e.g. as Serial1 RX/TX).
GPIO are not 5V tolerant on the P2 and Photon 2. Be sure the input voltage does not exceed 3.3V (typical).

Gen 2 Devices (E Series, Electron, Photon, and P2; does not include E404X):

All GPIO pins (A0..A7, D0..D7, DAC, WKP, RX, TX) can be used as long they are not used otherwise (e.g. as Serial1 RX/TX). On the Electron and E Series, there are additional GPIO B0..B5, C0..C5 as well.
On the Photon, Electron, and E Series, all GPIO pins except A3 and A6 are 5V tolerant. However you must not use INPUT_PULLUP or INPUT_PULLDOWN with 5V inputs.
On the P1, all GPIO pins except A3, A6, D0 and D1 are 5V tolerant. However you must not use INPUT_PULLUP or INPUT_PULLDOWN with 5V inputs.
On the P1 there are 2.1K hardware pull-up resistors to 3V3 on D0 and D1 and are not 5V tolerant.