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Old 08-10-2004, 11:35 PM
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Default Understanding Xilinx Timing Constraints Analysis Report

Hi all,

I am confused with the "Clock to Setup on destination clock " section of the
report. I am using differential clocks and the data doesn't seem right. Here
is an example:

Clock to Setup on destination clock clk_dco_N
| Src:Rise| Src:Fall| Src:Rise| Src:Fall|
Source Clock |Dest:Rise|Dest:Rise|Dest:Fall|Dest:Fall|
clk_dco_N | 5.280| | | |
clk_dco_P | 5.294| | | |

This seems to contradict to the achieved 4.7 ns clock period on the internal
clk_dco if I only understand correctly what this spec means... According to
the Xilinx Answer Database this means the Q of a flip-flop that is running
on one of the "source" clocks will reach the D of a flip-flop that is
running on the "destination" clock (in this case clk_dco_N) in no more than
"X"ns. Does this make sense at all for differential clocks?


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