SoftwareSerial: overflow()

// set up a new serial port
SoftwareSerial mySerial =  SoftwareSerial(rxPin, txPin);

mySerial.overflow()

#include <SoftwareSerial.h>
 
// software serial : TX = digital pin 10, RX = digital pin 11
SoftwareSerial portOne(10,11);
 
void setup()
{
  // Start the hardware serial port
  Serial.begin(9600);
 
  // Start software serial port
  portOne.begin(9600);
}
 
void loop()
{
  if (portOne.overflow()) {
   Serial.println("SoftwareSerial overflow!"); 
}