Can we use serial communication in arduino only for RX pin

Question

Can we use serial communication in arduino only for RX pin, so that I am free to use pin 1(TX) as digital I/O:

Serial.write('a');
pinMode(1,OUTPUT);
digitalWrite(1,LOW);

Answer 1

HardwareSerial takes over the Tx and Rx pins. However you can use SoftwareSerial.

Arduino forum user whiteglint143 made an adaptation of SoftwareSerial that does read-only.

http://gammon.com.au/Arduino/ReceiveOnlySoftwareSerial.zip

See Receive Only Software Serial - Arduino Forum

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You can regain control over the TX or RX pins by unsetting the TXENn or RXENn bit in the UCSRnB register.

Like this?

const byte LED = 1;
void setup ()
 {
 Serial.begin (115200);
 Serial.println ();
 UCSR0B &= ~bit (TXEN0); // disable transmit
 Serial.println ("Testing");
 pinMode (LED, OUTPUT);
 } // end of setup
void loop ()
 {
 digitalWrite (LED, HIGH);
 delay (500);
 digitalWrite (LED, LOW);
 delay (500);
 } // end of loop

Gerben's suggestion works, in a sense. The pin flashes, but rather disconcertingly, the Tx LED on the board also flashes, out of sync with pin 1. Clearly the signal is making its way to the ATmega16U2 chip, which then flashes the indicator LED. This may not be desirable if you have something connected to the serial port, as it may be interpreted as low-speed serial communications.

• Gerben: You can regain control over the TX or RX pins by unsetting the TXENn or RXENn bit in the UCSRnB register.
• Nick Gammon: Nice, simple solution! Good idea.
• Nick Gammon: See amended post, using that pin as a digital pin may have side-effects.
• Gerben: Great finding. Though calling Serial.println, after disabling TX is kind of silly.
• Nick Gammon: I hoped you wouldn't notice that. :P