Xilinx VHDL Attribute syntax error

Hello,

I was switching UCF lines to VHDL attributes when I came into this syntax error. Can someone suggest what the problem is?

#UCF file works fine INST cam2_x0_ibufd_inst DIFF_TERM = TRUE; INST cam1_x0_obufds IOSTANDARD=LVDSEXT_25;

-- VHDL attribute DIFF_TERM : boolean; attribute DIFF_TERM of cam2_x0_ibufd_inst:label is true; -- works attribute IOSTANDARD : string; attribute IOSTANDARD of cam1_x0_obufds:label is LVDSEXT_25; -- syntax error

begin

The syntax error is -- Undefined symbol 'LVDSEXT_25'

Thanks,

Brad Smallridge AiVision