From p 29 of the DS302 v1.4 Virtex 4 Data Sheet: DC and Switching
Characteristics, the output clocks from the DCM in the *high frequency mode*
shows 210-280 MHz capable FX outputs (for the slower -10 device) to pick up
where the *low frequency mode* drops off. The input for the high frequency
mode can be as low as 50 MHz if the DFS mode is all that's used.
100 MHz in, 100*M/N out up to 280 MHz in the -10 device.
Check to make sure you're 1) working in HF mode and 2) you're not using the
standard outputs - just the DFS.
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