In the Mux Data Hold CDC example, presented in the following figure, the multiplexer select signal is synchronized to the destination clock domain
clk_b and the
data_out is fed back to the multiplexer.
Figure 1. Mux Data Hold CDC Example
Similar to CE-controlled CDC, there is no restriction on how the multiplexer select signal is synchronized as long as it is reported as safe individually and the user is responsible for constraining the crossing delay on