Hi,
Did you tie all e DB0/SEL A, DB1/SEL B, and DB2/SEL C to VDRIVE? These pins are used to enable the DOUT A to DOUT C lines.
The conversion results go all zeros for when a CONVST pins is not used. How long did you pulse each CONVST for? Can you share some scope shots of your digital lines (CONVSTx, BUSY, /CS, SCLK, and DOUTx) so we can take a closer look?
Regards,
Karen