Hi,
When using the DDR functionality, is it the user's responsibility to provide the phase-shifted clocks or does the above mentioned primitive do this for me? The documentation is not very clear.
Although using a DLL to phase-shift is the best practice, can I get by just using an inverter between the two clocks? If so, does the Virtex-II IOB provide a "free" inverter (gets absorbed in the IOB)?
Comments?
Anil
The primitive has two clock inputs, they should both be connected.
Yes. You can connect clk to one input and !clk to the other and the inverter is sucked into the IOB. Note that many people still use the
0 and 180 clock outputs from a DCM to do this which requires two global clock buffers. Also remember that to work reliably with a single clock and its inversion, your clock needs to have a 50% duty cycle.Have something to add? Share your thoughts — no account required.
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