Arduino IDE 1.5.7 serial test sketch

testsketch.ino

int modes[30] = {
    SERIAL_5N1,    
    SERIAL_5E1,    
    SERIAL_5O1,    
    SERIAL_5N2,    
    SERIAL_5E2,    
    SERIAL_5O2,    
    
    SERIAL_6N1,    
    SERIAL_6E1,    
    SERIAL_6O1,    
    SERIAL_6N2,    
    SERIAL_6E2,    
    SERIAL_6O2,    
    
    SERIAL_7N1,    
    SERIAL_7E1,    
    SERIAL_7O1,    
    SERIAL_7N2,    
    SERIAL_7E2,    
    SERIAL_7O2,    
    
    SERIAL_8N1,    
    SERIAL_8E1,    
    SERIAL_8O1,    
    SERIAL_8N2,    
    SERIAL_8E2,    
    SERIAL_8O2,
    
    SERIAL_9N1,    
    SERIAL_9E1,    
    SERIAL_9O1,    
    SERIAL_9N2,    
    SERIAL_9E2,    
    SERIAL_9O2    

};

int limits[5] = {
    0x1F,       // 5 bit
    0x3F,       // 6 bit
    0x7F,       // 7 bit
    0xFF,       // 8 bit
    0x1FF,      // 9 bit
};


void setup() {
    // Serial connectio over UART for test output    
    Serial.begin(115200);

    delay(5000);
}

int counter = 0;

void test_usart(int mode, int limit) {

    // set up the USARTS 
    Serial1.begin(9600, modes[mode]);
    Serial2.begin(9600, modes[mode]);
    Serial3.begin(9600, modes[mode]);

      for(int i=0; i <= limits[limit]; i++) {
        Serial1.write(i);
        Serial2.write(i);
        Serial3.write(i);   
        
        counter++;
        
        while(!Serial1.available());
        while(!Serial2.available());
        while(!Serial3.available());

        int result1 = Serial1.read();
        int result2 = Serial2.read();
        int result3 = Serial3.read();

        if(result1 == i) {
            Serial.print("Serial1 sent ");
            Serial.print(i, HEX);
            Serial.print(", received ");
            Serial.print(result1, HEX);
            Serial.println(", OK! ");
        } else {
            Serial.print("Serial1 sent ");
            Serial.print(i, HEX);
            Serial.print(", received ");
            Serial.print(result1, HEX);
            Serial.println(", >>>> FAIL <<<< ");
        }
        
        if(result2 == i) {
            Serial.print("Serial2 sent ");
            Serial.print(i, HEX);
            Serial.print(", received ");
            Serial.print(result2, HEX);
            Serial.println(", OK! ");
        } else {
            Serial.print("Serial2 sent ");
            Serial.print(i, HEX);
            Serial.print(", received ");
            Serial.print(result2, HEX);
            Serial.println(", >>>> FAIL <<<< ");
        }
        
        if(result3 == i) {
            Serial.print("Serial3 sent ");
            Serial.print(i, HEX);
            Serial.print(", received ");
            Serial.print(result3, HEX);
            Serial.println(", OK! ");
        } else {
            Serial.print("Serial3 sent ");
            Serial.print(i, HEX);
            Serial.print(", received ");
            Serial.print(result3, HEX);
            Serial.println(", >>>> FAIL <<<< ");
        }

        Serial.print(counter, DEC);
        Serial.println(" bytes sent");
        
    }
    
}

void loop() {
  // put your main code here, to run repeatedly:    
  
    // for each frame width
    for(int i=0; i<4; i++) {
        // for each mode in this frame width
        for(int j=0; j<6; j++) {
            Serial.print("Test mode ");
            Serial.println(i*6 + j, DEC);
            test_usart(i*6 +j, i);
            delay(500);
        }
    }
       
    delay(1000);
}

This is the sketch i used to test the Serial ports of the Arduino Due.