Hi, yk.
Do you see this problem on multiple parts? Are you using the AD7949 evaluation board? Which mode are you trying to use RDC/RAC/RSC with or without busy indicator?
Note that there is always a one deep delay when writing the CFG register. From power-up, in any read/write mode, the first three conversion results are undefined because a valid CFG does not take place until the 2nd EOC; thus two dummy conversions are required.
Regards,
Karen