During a behavioral simulation of the CIC Compiler, output goes to "X" every time the RDY output is low. Why?
This is by design in the CIC Compiler v1.2. When the RDY output is low, the data output should be ignored.
The next release of the IP core will not display Xs when RDY is low.
This issue is resolved in 11.3 with the latest version of the CIC Compiler v1.3.