描述

Do CoolRunner devices have weak pull-up resistors on their I/Os?

解决方案

CoolRunner XPLA3 devices have pull-up resistors on the I/O pins, which can be activated on a pin-by-pin basis for inputs only. CoolRunner-II devices also have pull-up resistors on the I/O pins. For further details, see (Xilinx Answer 14318). You can configure these in the Xilinx Constraints Editor or in a User Constraints File (UCF). The UCF syntax is as follows:

NET signalname PULLUP;

These pull-up resistors can also be used on unused I/O to prevent unused pins from floating:

- In the 5.1i software, this option is located under the "Fit" process -> "Basic" tab -> "Unused Pin Termination".

- In the 4.1i software, this option is located under the "Generate Programming File" process.