When I implement a design, a warning message similar to one of the following occurs:
What do these warning messages mean? What termination methods are available in a CoolRunner-II device?
The CoolRunner-II device includes a central "global termination" circuit that can be enabled as a keeper (bus-hold) circuit or as a pull-up.
This circuit can optionally be connected to any I/O pin on a pin-by-pin basis. Because there is only one global termination circuit, this means that pull-ups and keeper circuits cannot be enabled simultaneously in the same design.
The warning message describes this conflict and warns that the pull-up termination request is ignored in favor of bus-hold because the hardware cannot enable both circuits.
When checking for these conflicts, consult the "Unused I/O Pad Termination Mode" and "Input and Tristate Termination Mode" options in the ISE properties menu (Fitting tab/category), as well as any user-declared termination settings.
The table below shows which termination modes can be used together.
You can use the following UCF constraint to enable pull-ups:
net datain pullup;
You can use the following UCF constraint to enable bus-hold (keeper) circuitry:
net datain keeper;