Due USB-Serial Communication fails (programming works)

Hello everyone,

I recently purchased an Arduino Due and have been trying for a few days now to get the Serial-USB connection to work. I was able to properly install the Arduino drivers and I have no problem programming the board over the Serial-USB connection. However, as soon as I attempt to use the Serial functionality in a programm, the USB connection ceases to work. While my program is running, I can still see the Arduino as a COM device, but no Serial data shows up through the Serial Monitor or through the Windows 7 PowerShell. If someone could give me guidance as to what might be wrong, I would be very greatful. Here is a list of symptoms and what I have tried so far:

  • System Specs: Windows 7 Home Professional, x64, running as a non-administrator account.

  • Using Arduino 1.5.7 Beta IDE.

  • I am using the USB cable that came with my Nexus 7.

  • Programming the Due over USB works fine on both the native USB port and the programming port

  • Pin 1 (TX) is outputting a signal when I call Serial.Write(), as I have tested by connecting pin 1 to pin 2 and setting pin 2 to a RISING interrupt.

  • Windows PowerShell shows that there are no bytes to read on the Due’s Virtual COM Port (COM4)

  • Data transmission from computer to Due also does not seem to work, as Serial.available never rises above zero.

  • I have attempted updating the FDTI drivers from the FDTI website but this does not fix the problem.

  • I have tried running the IDE as administrator.

  • I have tried using both the native and programming ports for Serial communication, even though my understanding is that only the native port supports it.

The code I am using to test the connection:

volatile int itrCount = 1;

void setup() {
  // put your setup code here, to run once:
  while (!Serial);

void loop() {
  // put your main code here, to run repeatedly:
  if (Serial.available() > 0) {
    char datIn = Serial.read();
    Serial.print("I got: ");

void wait_for_contact() {
  while (Serial.available() <= 0)
    Serial.println('A'); //Send char 65'

void interrupt()

Any help would be greatly appreciated.

bump anyone? :frowning:

Update: I tried the Due on another computer using the same USB cable and the problem persisted. I was able to program, but serial did not work. I am wondering whether the FDTI chip is broken.

I too am having a similar issue and seem to have tracked it down to the attachInterrupt call.

In short, I am trying to use and external interrupt to trigger SerialUSB.write. If I remove the attachInterrupt call I can connect and communicate via the native usb port no problems.

Any ideas?

#include <DueTimer.h>

int const numPnts = 1024;
int16_t read_times[2][numPnts];
int16_t values[2][numPnts];

volatile unsigned int i;
volatile int curBuf;
volatile int oldBuf; 
volatile unsigned long startTime;
volatile unsigned long curTime;

const int extTrigPin = 31;

bool printValues = false;

void setup() 
  pinMode(A0, INPUT);

  //if I comment the following two lines and add the attachInterrupt the SerialUSB call does not work.
  Timer1.start(24); // Calls every 24us
  curBuf = 0;
void reset_values(){
  i = 0;//reset to zero
  oldBuf = curBuf;//switch bufferID
  curBuf = 1 - curBuf;//transform curBuf between 0 and 1
  startTime = micros();//first start time for measurement (NOTE REPLACED IN daq_loop())
  printValues ^= 1;//change print flag to send out values
//  int j;
//  for(j=0;j<100;j++) {
//    Serial.print(j);
//    Serial.print("   ");
//    Serial.println(values[oldBuf][j]);
//  }
//  Serial.print(oldBuf);
//  Serial.print("   ");
//  Serial.print(curBuf);
//  Serial.print("   ");
//  Serial.println("DONE!");

void daq_loop(){
  curTime = micros();
  values[curBuf][i] = analogRead(A0);
  read_times[curBuf][i] = curTime-startTime;
  startTime = curTime;
//  Serial.print(i);
//  Serial.print("   ");
//  Serial.print(values[curBuf][i]);
//  Serial.print("   ");
//  Serial.println(curBuf);


void loop() 
  if (printValues){  // print out the results
    SerialUSB.write((uint8_t *)values[oldBuf],2048);
    SerialUSB.write((uint8_t *)read_times[oldBuf],2048);//is this the best way or should we pack into 2D array?
    printValues ^= 1;

This topic is a bit old but I got this problem too and found a solution.
The workaround I found is to change the priority of attachInterrupt in WInterrupts.c

Go to : C:\Program Files (x86)\Arduino\hardware\arduino\sam\cores\arduino

Or if you can't find this folder it should be there :

Open WInterrupts.c and change the priority on line 41, 47, 53 and 59 like this :
NVIC_SetPriority(PIOA_IRQn, 1); //was 0

Hope it helps!