digitalWrite()

Input/Output

Write a HIGH or a LOW value to a GPIO pin.

// PROTOTYPE
void digitalWrite(uint16_t pin, uint8_t value)

If the pin has been configured as an OUTPUT with pinMode() or if previously used with analogWrite(), its voltage will be set to the corresponding value: 3.3V for HIGH, 0V (ground) for LOW.

digitalWrite() takes two arguments, pin: the number of the pin whose value you wish to set and value: HIGH or LOW.

digitalWrite() does not return anything.

// EXAMPLE USAGE
int LED = D1;              // LED connected to D1

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

void loop()
{
  digitalWrite(LED, HIGH); // sets the LED on
  delay(200);              // waits for 200mS
  digitalWrite(LED, LOW);  // sets the LED off
  delay(200);              // waits for 200mS
}

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 output as long they are not used otherwise (e.g. as Serial1 RX/TX).
For the B-Series SoM all GPIO pins (A0..A7, D0..D13, D22, D23) can be used for digital output 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 output 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.
The default drive strength on Gen 3 devices is 2 mA per pin. This can be changed to 9 mA using pinSetDriveStrength().

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).
Pins D0 and D1 can be used as analog inputs on the P2 (A3 and A4) if I2C is not being used.
The drive strength on the P2 and Photon 2 is 4 mA per pin in normal drive and 12 mA per pin in high drive mode. Drive strength selection is only available in Device OS 5.5.0 and later. There is a maximum of 200 mA across all pins. On the P2, the total maximum could be further limited by your 3.3V regulator.

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). For the Electron and Series B0..B5, C0..C5 can be used as well.
The drive current on Gen 2 devices is 25 mA per pin, with a maximum of 125 mA across all GPIO.