Input/Output

pinMode()

pinMode() configures the specified pin to behave either as an input (with or without an internal weak pull-up or pull-down resistor), or an output.

// SYNTAX
pinMode(pin,mode);

pinMode() takes two arguments, pin: the number of the pin whose mode you wish to set and mode: INPUT, INPUT_PULLUP, INPUT_PULLDOWN or OUTPUT.

pinMode() does not return anything.

// EXAMPLE USAGE
int button = D0;                      // button is connected to D0
int LED = D1;                         // LED is connected to D1

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

void loop()
{
  // blink the LED as long as the button is pressed
  while(digitalRead(button) == HIGH) {
    digitalWrite(LED, HIGH);          // sets the LED on
    delay(200);                       // waits for 200mS
    digitalWrite(LED, LOW);           // sets the LED off
    delay(200);                       // waits for 200mS
  }
}

getPinMode(pin)

Retrieves the current pin mode.

// EXAMPLE

if (getPinMode(D0)==INPUT) {
  // D0 is an input pin
}

digitalWrite()

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

// SYNTAX
digitalWrite(pin, 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
}

digitalRead()

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

// SYNTAX
digitalRead(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
}

analogWrite()

Writes an analog value (PWM wave) to a pin. Can be used to light a LED at varying brightnesses or drive a motor at various speeds. After a call to analogWrite(), the pin will generate a steady square wave of the specified duty cycle until the next call to analogWrite() (or a call to digitalRead() or digitalWrite() on the same pin). The frequency of the PWM signal is approximately 500 Hz.

// SYNTAX
analogWrite(pin, value);

// EXAMPLE USAGE

int ledPin = D1;               // LED connected to digital pin D1
int analogPin = A0;            // potentiometer connected to analog pin A0
int val = 0;                   // variable to store the read value

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

void loop()
{
  val = analogRead(analogPin); // read the input pin
  analogWrite(ledPin, val/16); // analogRead values go from 0 to 10223,
                               // analogWrite values from 0 to 255.
  delay(10);
}

When used with these pins, the analogWrite function has nothing to do with the analog pins or the analogRead function.

analogWrite() takes two arguments, pin: the number of the pin whose value you wish to set and value: the duty cycle: between 0 (always off) and 255 (always on).

NOTE: pinMode(pin, OUTPUT); is required before calling analogWrite(pin, value); or else the pin will not be initialized as a PWM output and set to the desired duty cycle.

analogWrite() does not return anything.

analogRead()

Reads the value from the specified analog pin. The device has 6 channels (A0 to A5) with a 10-bit resolution. This means that it will map input voltages between 0 and 3.6 volts into integer values between 0 and 1023. This yields a resolution between readings of: 3.6 volts / 1024 units or, 0.0035 volts (3.5 mV) per unit.

// SYNTAX
analogRead(pin);

analogRead() takes one argument pin: the number of the analog input pin to read from ('A0 to A5'.)

analogRead() returns an integer value ranging from 0 to 1023.

// EXAMPLE USAGE
int ledPin = D1;                // LED connected to digital pin D1
int analogPin = A0;             // potentiometer connected to analog pin A0
int val = 0;                    // variable to store the read value

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

void loop()
{
  val = analogRead(analogPin);  // read the input pin
  analogWrite(ledPin, val/16);  // analogRead values go from 0 to 1023, analogWrite values from 0 to 255
  delay(10);
}