ADIS16209 Datasheet
The address code in the SPI protocol is missing its most significant bit.
The next revision of this datasheet will insert "A6" into the two areas of yellow highlight. Until then, please be assured that this bit is active and that you can read the PROD_ID register, using DIN = 0x4A00 to request the contents of this register (which will flow out on DOUT, during the following 16-bit SPI sequence).
The ADIS16209 datasheet now contains the SOLUTION from this disclosure.