Re: Clocking in a virtex 2 without using the clock trees : questions

> Hi, > > I have a serial bus coming in a Virtex II -5 in LVDS format at 80 MHZ > with 3 data in parallel. The data change on the falling edge of the > clock. The problem is that the clock is present only when data is > transmitted (no DCM possible) and the pads used for the clock does not > allow the use of a bufgp without an important routing delay. I am > using the MAXSKEW constraint on the received clock and the best I can > get is 450 ps (I can not use the local clock resources described in > xapp609). This clock goes to approximately 40 FFs. I have, on this > clock domain, among other things, a shift register so I have a FF to > FF path. When having the min skew of 450 ps parts of the shift > register are implemented in the same CLB so the output of a FF goes > through the local routing matrix of the CLB and back to the input of a > FF in the same CLB : I believe it must be the shortest and quickest > path to go from one FF to another. My problem is that I wonder if the > skew I have will always be smaller than the clock_to_out + prop_delay > : I believe the max values are ok but what about typical ? > > Thank you. > > J.F. Hasson
Reply to
Peter Alfke
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Hi,

Unfortunatly, I can not drive a global buffer with this clock because the maximum delay I get when I go by the global buffer is 8 ns which is incompatible with the fact that data is synchronous to the falling edge of the 80 MHz clock. I believe I will try something else with a much faster clock but just if this information is available what is the maximum skew provided by the clock tree in a Virtex II ? The reason for my question is that I read in a previous post that is was below 100 ps but when I run the timing analyzer it seems it is more like 300 ps. Did I miss something ? If not is my 450 ps skew small enough to consider no extra effort necessary ?

Thanks,

J.F. Hasson

"Peter Alfke" a écrit dans le message de news: snipped-for-privacy@xilinx.com...

Reply to
jean-francois hasson

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