Answers Database M1.5 9500/XLConstraints Editor: Clock pads using BUFG symbol not visible in Constraint Editor Record #4246 Product Family: Software Product Line: M1 Implementation Product Part: Constraints Editor Problem Title: M1.5 9500/XLConstraints Editor: Clock pads using BUFG symbol not visible in Constraint Editor Problem Description: Urgency: Standard General Description: A CPLD design contains a clock pad assigned to a global clock using a BUFG symbol. The clock pad doe s not appear in the Global tab of the Constraints Editor. You can't create any Period, Pad-to-Setup or Clock-to-Pad timespecs relative to that clock in any of the tabs of the Constraints Editor. Solution 1: For CPLD, clock pads are only recognized by the Constraints Editor if they are buffered using an ord inary IBUF, but by BUFG. To assign a clock to a global clock (GCK) pin so that it will be recognized   by the Constraints Editor, use an IBUF symbol and apply the "BUFG=CLK" property to the clock pad ne t or the IBUF instance. You can apply the BUFG=CLK property either in the design (netlist) or by han d-editing the UCF file. (The BUFG property cannot be entered using the Constraints Editor.) End of Record #4246 - Last Modified: 05/26/99 08:51

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