我用xilinx spartan6做一个摄像头显示的东西，发现一个奇怪的现象，如果设置cdc文件，用chipscope去测量FV场信号，LV行信号的话，就显示正常，如果取消cdc文件，则显示是扭曲的画面，不是是怎么回事呢？输入的FV,LV端口都做了buff处理啊，如下代码：
Inst_IOBUF_CAMA_FV : IOBUF
generic map (
DRIVE => 12,
IOSTANDARD => "DEFAULT",
SLEW => "SLOW")
port map (
O => CAMA_FV_I_Buf, -- Buffer output
IO => CAMA_FV_I, -- Buffer inout port (connect directly to top-level port)
I => '0', -- Buffer input
T => dummy_t -- 3-state enable input, high=input, low=output
);
Inst_IOBUF_CAMA_LV : IOBUF
generic map (
DRIVE => 12,
IOSTANDARD => "DEFAULT",
SLEW => "SLOW")
port map (
O => CAMA_LV_I_Buf, -- Buffer output
IO => CAMA_LV_I, -- Buffer inout port (connect directly to top-level port)
I => '0', -- Buffer input
T => dummy_t -- 3-state enable input, high=input, low=output
);
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