Free up RX pin while still sending on TX?

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

It doesn't seem possible to free up the RX pin while using the serial port, using the Arduino API. Anyone know if it is possible to still use the RX pin as a DIO while still using the serial port on TX, by writing some fancy AVR code?

Thanks,
Drew

2

I figured it out. One register modification will switch off just the RX half of the serial module.

Cheers!
Drew

// Demonstration of how to simultaneously use the RX pin as DIO while using the TX pin for serial output.
// You should get recurring good news in the Serial Monitor.
// You should be able to measure the RX pin turning on and off in sync with the pin 13 LED.
// (For some reason the RX LED doesn't blink like I'd expected, but that's no big deal.)

#define RXPIN 0 // The arduino pin for RX
#define TXPIN 1 // The arduino pin for TX

void setup()
{
  // Set up the serial port.
  Serial.begin(9600);  // Turns on both TX and RX
  //  UCSR0B = (1<<RXEN0)|(1<<TXEN0);
  UCSR0B = (1<<TXEN0);  // Note: this one line might be enough to free up the RX pin.

  // enable interrupt on complete reception of a byte
  //sbi(UCSR0B, RXCIE0);

  pinMode(RXPIN, OUTPUT);

}

void loop()
{
  Serial.println("Still able to send stuff over TX!");
  
  // See if we can blink the RX pin while still sending stuff on the TX pin.
  int ledPin = 13;
  digitalWrite(ledPin, HIGH);   // sets the LED on.
  digitalWrite(RXPIN, HIGH);
  delay(1000);                  // waits for a second
  digitalWrite(ledPin, LOW);
  digitalWrite(RXPIN, LOW);  // sets the LED off
  delay(1000);                  // waits for a second

}