dll spartan 2
The dedicated clock input pin along with its correspondent clock i/o buffer in one thing, and the internal global clock distribution net is another. They can be connected directly or through DLL. If connected directly, different time delays can appear between different clock nets, depending on the loads. The DLL's main purpose (when is connected) is to ensure a low skew clock distribution inside the chip, using the internal clock distribution networks, by monitoring the output clock with a feedback input. Check the Xilinx Spartan2 datasheet, page 20, module 2.
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