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This example is for Wiring version 0024+. If you have a previous version, use the examples included with your software. If you see any errors or have comments, please let us know.

Simple Read
Read data from the serial port and turn ON the onboard LED if the character received is an 'a'

    int val;          // to read the char
    int ledPin = 48;  // onboard led pin

    void setup() {
      Serial.begin(9600);
      pinMode(ledPin, OUTPUT);
    }

    void loop() {
      if(Serial.available()) {         // if data available
        val = Serial.read();           // read data
        if(val == 'a') {               // if value read is character 'a'
          digitalWrite(ledPin, HIGH);  // turn ON the onboard LED
        } else {
          digitalWrite(ledPin, LOW);   // if not turn it OFF
        }
      }
      delay(100);  // wait 100ms for next read
    }