Hello,
I have a question about the OFFSET In constraint.
To my mind, OFFSET In is the same thing that the set-up time. But what about the hold time ?
If I want to have a bigger hold time, I need to decrease my OFFSET In constraint ??
Or the only thing I can do is playing with the clock skew or data path delay ?
Tk.
For full details about the OFFSET constraint, read the constraint guide. It is in your ISE directory: $Xilinx\doc\usenglish\books\docs \cgd.
If you want to specify hold time, you will use:
OFFSET = IN VALID BEFORE ;
where the hold time is the data valid window - the setup time.
For example:
TIMEGRP TNM_CTRL_INPUTS OFFSET = IN 3ns VALID 3ns BEFORE fpga_0_CLK;
Specifies 3ns setup and 0 hold.
TIMEGRP TNM_CTRL_INPUTS OFFSET = IN 3ns VALID 4ns BEFORE fpga_0_CLK;
Specifies 3ns setup and 1ns hold.
Regards,
John McCaskill
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