如何在IOB中为spartan-3生成FPGA使用TFF？

亲爱的大家！
如何在IOB中为spartan-3生成FPGA使用TFF（TFF1和TFF2三态触发器）？
我想在spartan-3 FPGA（Spartan-3 GenerationFPGA用户指南）的IOB中有两个三态触发器（TFF1和TFF2），现在我想使用它们，但这些都不是关于此的文档。
请帮帮我！
谢谢！！



以下为原文

Dear everybody!
    How can I use TFF(TFF1 and TFF2 Three-State flip-flop) within the IOB for spartan-3 Generation FPGA?
    I fount there are two three-state flip-flop(TFF1 and TFF2) within the IOB of the spartan-3 FPGA(Spartan-3 Generation
FPGA User Guide) and now I want to use them,but these is no document about this.
   Please help me! thanks!!