pinMode(66, OUTPUT); Causes Strange Behavour on Due DAC0, how do you reset the pin mode?

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pinMode(66, OUTPUT); Causes Strange Behavour on Due DAC0, how do you reset the pin mode?

I'm creating a project using the Arduino Due's DAC. For reasions related to the project I at some times want to be able to set the DAC0 pin to LOW.

I've noticed strange behaviour when using the command:
pinMode(66, OUTPUT);

Without the command present I see a nice output signal on an oscilloscope consistent with what I'm aiming for:
(sorry I can only include one image)

However if pinMode(66, OUTPUT); is used I get a flickering result:

Does anyone know what state the DAC0 pin mode is set to as default and what command can put it back into that state?

I have tested pinMode set to INPUT and INPUT_PULLUP and they both give similar problems.

If it helps please find some sample code below:

// True Due DAC Range 0.54V 2.74 V

void setup() {
  // resolution to 12, you can use analogWrite() with values between 0 and 4095
  // default resolution to 8, you can use analogWrite() with values between 0 and 255
  analogWriteResolution(12);
  //Serial.begin(115200);//Set the baudrate to 115200,same as the software settings
  pinMode(66, OUTPUT);
  // pinMode(66, INPUT);
  // pinMode(66, INPUT_PULLUP);  
}

void moveRight(int x) {
  int y;
  for (int y = x; y > 0; y = y - 1) {
    // right
    analogWrite(DAC0, 0);   //0.54V -low part
    delayMicroseconds(80);  //low duration . Should be 80us

    for (int i = 117; i < 4095; i = i + 117) {  //should be 140us
      analogWrite(DAC0, i);                     // makes a linear rise t=140us, x=4us, +117 each step, loop=35
      delayMicroseconds(4);
    }

    analogWrite(DAC0, 4095);  //high period. Should be 160us
    delayMicroseconds(160);
  }
}

void moveLeft(int x) {
  int y;
  for (int y = x; y > 0; y = y - 1) {
    //left
    analogWrite(DAC0, 4095);  //high period. Should be 160us
    delayMicroseconds(160);

    for (int i = 4095; i > 0; i = i - 117) {  //should be 140us
      analogWrite(DAC0, i);                   // makes a linear rise t=140us, x=4us, +117 each step, loop=35
      delayMicroseconds(4);
    }

    analogWrite(DAC0, 0);   //0.54V -low part
    delayMicroseconds(80);  //low duration . Should be 80us
  }
}

void loop() {
  analogWrite(DAC1, 0);  //0.54V -Use DAC1 to give ground reference?
  moveRight(1);
  // pinMode(66, OUTPUT);
  // digitalWrite(66, LOW);
  // delayMicroseconds(200);
  // digitalWrite(66, HIGH);
  // delayMicroseconds(200);
}