xp2syscloclkpll

代码说明：

  这个是讲pll的具体用法的,一般在fpga设计中都会用到 他,这个是lattice的xp2的pll的介绍,不过,fpga 都是相通的其他两家也差不多(Pll say this is the specific usage, the general design in the FPGA will use him, this is the lattice of the pll of xp2 introduction, however, fpga are connected to other two similar)