The termination resistors are specified for values in the ATA/ATAPI-6 specification 4.7K resistors. However our tailgate reference design boards are intended for short (or no) cable length. Our tests have shown that either the 4.7K or 1K ohm resistors work well for the short or no cable scenarios. However the CY3671 development kit board expects the use of longer cables and uses the 4.7K resistor for the IORDY line.
The use, and selection of value, of resistors is a cost-based issue. One needs to guarantee the signal quality per the spec especially based on your cabling requirements. For UDMA it is best to follow the spec closely.