AD5560 ACCESS

Dear Sir or Madam

If only  the DVCC of AD5560   be supplied by 3.3V , refer to DGND .  Can I access the all the  registers ?

For there is a phenomenon  ,  sometimes , if I disable the negative power rail which supplies AVss , HCAVss  of AD5560 . The registers we read will be all 0x0000 , as opposed to the case which the negative power is enabled . 

Thank you in advance for your tips about above .

kindly regards

Anglic