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Entering values in the constraint manager in timing and in length

CADcaveman
There used to be a problem with entering values in timing and length in constraint manager. Can someone please tell me if I can reliably design a board with values in the constraint manager in both timing and length?
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  • DaleinAZ

    Well, you obviously can't enter both timing and length constraints on the same net(s). Given an assumed prop delay (in ns/inch), one is a direct ratio of the other. Plus you could create impossible constraints like min length of 12 inches and max delay of 1.5ns.

    I suppose you could constrain one net by length and another (unrelated) net by time, although I have never tried this.

    Given that prop delay can vary by layer and material, why not just constrain by time? That is ultimately what you want to control. That way, if you change material or stackup, it will automatically correct to give the time desired.

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  • DaleinAZ

    Well, you obviously can't enter both timing and length constraints on the same net(s). Given an assumed prop delay (in ns/inch), one is a direct ratio of the other. Plus you could create impossible constraints like min length of 12 inches and max delay of 1.5ns.

    I suppose you could constrain one net by length and another (unrelated) net by time, although I have never tried this.

    Given that prop delay can vary by layer and material, why not just constrain by time? That is ultimately what you want to control. That way, if you change material or stackup, it will automatically correct to give the time desired.

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