FPGA设计遇到PAR错误

你好-
我正在修改已经放置在电路板上的FPGA的设计。
该项目必须从旧版本（9.1，我相信）升级为ISE 10.1。
升级后，我能够成功合成并实施项目。
到目前为止，我已经进行了一些设计更改并完成了几个实现错误，但我目前仍然遇到以下PAR错误：
错误：放置：704  -  IPAD组件“FPGA_CLK_N”被锁定到MONITORIPAD站点“IOB_X1Y98”。
IPAD类型的组件无法锁定到MONITORIPAD类型的站点
错误：放置：704  -  IPAD组件“FPGA_CLK_P”被锁定到MONITORIPAD站点“IOB_X1Y99”。
IPAD类型的组件无法锁定到MONITORIPAD类型的站点
任何人都可以提出一些如何解决这个问题的建议吗？
我的ucf文件中的相关信息是：
Net“FPGA_CLK_P”TNM_NET = FPGA_CLK_P;
tiMESPEC TS_FPGA_CLK_P = PERIOD FPGA_CLK_P 6.4 ns高50％;
净“FPGA_CLK_N”TNM_NET = FPGA_CLK_N;
TIMESPEC TS_FPGA_CLK_N = PERIOD FPGA_CLK_N 6.4 ns高50％;
NET“FPGA_CLK_P”LOC = A14 |
IOSTANDARD =“LVDS_25”|
DIFF_TERM = TRUE;
NET“FPGA_CLK_N”LOC = A13 |
IOSTANDARD =“LVDS_25”|
DIFF_TERM = TRUE;
正如我所说，这是一块已经在板上的芯片，因此更改引脚排列不是一种选择。
在此先感谢任何帮助......



以下为原文

Hello-

I am modifyng a design for an FPGA that was already placed on a board.  The project had to be upgraded for ISE 10.1 from an older version (9.1, I believe).  I was able to successfully synthesize and implement the project after it was upgraded.

I had made some design changes and have worked through a couple of implementation errors so far, but I'm currently stuck on the following PAR error:

ERROR:Place:704 - IPAD component "FPGA_CLK_N" is locked to MONITORIPAD site "IOB_X1Y98". A component of type IPAD can
   not be locked to a site of type MONITORIPAD
ERROR:Place:704 - IPAD component "FPGA_CLK_P" is locked to MONITORIPAD site "IOB_X1Y99". A component of type IPAD can
   not be locked to a site of type MONITORIPAD

Can anyone offer some suggestions as to how to resolve this?

The relevant info from my ucf file is:

Net "FPGA_CLK_P" TNM_NET = FPGA_CLK_P;
TIMESPEC TS_FPGA_CLK_P = PERIOD FPGA_CLK_P 6.4 ns High 50%;
Net "FPGA_CLK_N" TNM_NET = FPGA_CLK_N;
TIMESPEC TS_FPGA_CLK_N = PERIOD FPGA_CLK_N 6.4 ns High 50%;

NET "FPGA_CLK_P" LOC = A14 | IOSTANDARD = "LVDS_25" | DIFF_TERM = TRUE;
NET "FPGA_CLK_N" LOC = A13 | IOSTANDARD = "LVDS_25" | DIFF_TERM = TRUE;

As I said, this is a chip that is already on a board, so changing the pinout is not an option.

Thanks in advance for any assistance...