説明

When I implement a design, a warning message similar to one of the following occurs:

"Warning:CPLD:960: - PULLUP specified for net DATAIN conflicts with previous KEEPER specification. PULLUP is ignored."

"Warning:CPLD:962: - KEEPER specified for net DATAIN conflicts with previous PULLUP specification. PULLUP is ignored."

What do these warning messages mean? What termination methods are available in a CoolRunner-II device?

ソリューション

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.

Notes:

1. In all these combinations, individual User I/O can have Keeper termination alone.
2. In all these combinations, individual User I/O can have Pull-up termination alone.
3. In all these combinations, individual User I/O can have either Keeper or Pull-up (not both in same design) termination.

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;