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Visitor
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Registered: ‎01-23-2008

Is adjustment for setup/hold times required if input standards are different from default but same for both clk and data

I'm curious about subject for Virtex-5. There's some ambiguilty to me in datasheet.

 

For Spartan-3 there were phrases for both modes - with DCM and w/o any DCM:

- "This setup time requires adjustment whenever a signal standard other than LVCMOS25 is assigned to the Global Clock Input or the data Input. If this is true of the Global Clock Input, subtract the appropriate adjustment from Table 43. If this is true of the data Input, add the appropriate Input adjustment from the same table." 

- "This hold time requires adjustment whenever a signal standard other than LVCMOS25 is assigned to the Global Clock Input or the data Input. If this is true of the Global Clock Input, add the appropriate Input adjustment from Table 43. If this is true of the data Input, subtract the appropriate Input adjustment from the same table. When the hold time is negative, it is possible to change the data before the clock’s active edge."

 

So if input standards were same for both clk and data - no adjustment were required since same value were added and substracted.

 

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For Virtex-5 I found phrase  "For situations where clock and data inputs conform to different standards, adjust the setup and hold values accordingly using the values shown in IOB Switching Characteristics, page 32." ONLY for table 97 "Global Clock Setup and Hold With DCM and PLL in Source-Synchronous Mode"

 

The question is: is it true for different modes? (I guess it's true - just need to clear things)

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