Do CoolRunner devices have internal pull-ups or pull-down resistors?
The XPLA3 family of devices (XCR3000XL parts) have internal pull-up resistors that have been characterized to be approximately 60k to 150k Ohms.
They may be utilized only in a design on input signals (no bidirectional or output signals). To access them, you must enter the signals on which you wish the pull-ups to be active in a UCF file:
NET mysignala PULLUP;
NET mysignalb PULLUP;
Alternatively, this can also be done through the Constraints Editor.
You will then see a "PU" in the fitter report for those signals, indicating that the pull-up resistor is active.
Obsolete XPLA devices
The XPLA1 and XPLA2 families in the 32A, 64, and 128-macrocell devices have internal pull-down resistors that are automatically activated by the fitter for outputs that are "no connects". These pull-downs cannot be implemented on active or "used" I/O. The values of the pull-downs are not guaranteed, but by characterization, they range from approximately 50k to 200k Ohms.
The 32 and 32C-macrocell parts do not have internal pull-down resistors. It is important for end users to properly terminate all unused inputs so that the CMOS inputs do not float into the linear region.
It is recommended that all unused inputs be terminated with a 10k pull-up resistor on the 32-macrocell devices. Unused I/O can be forced Low or High (as an output) or have external pull-up/down resistors to ensure that pin drift does not occur.