LTC2323 16bit

I drive  ltc2323 at 5MSPS rate with fpga code  ,and refer to the driven code which ADI offered.but there is a big porblem:the timing of signal sck and cnv signals are right and comply with the spec ,but I can't get back the adc value no matter what I do  ,so I think there must be something wrong with  my code .However ,I think my code is as same as ADI offered ,I don't know what's the reason lead to this situation。