Arduino Due DAC output value not zero

Hello,

I am using Arduino Due to do some control via the DAC pin. However, when I set the DAC output to be 0, the actual value is not zero but some value around 0.6V. My code is as below :

void loop() {
// put your main code here, to run repeatedly:
analogWriteResolution(8);
analogWrite(DAC1, 0);

}

Is there anything that I missed out? Thank you.