ise 综合的错误，有知道的吗?

今天综合出错，但是找不出原因，有知道的麻烦跟贴说一说啊。。。

ERROR:Xst:528 - Multi-source in Unit <top> on signal <datainout1<7>>
Sources are:
   Dangling signal <pp/clkout> in Unit <ps2> is tied to 0 by XST
   Dangling signal <ll/datain1<0>> in Unit <lcd> is tied to 0 by XST

有多个输入源，检查一下》