Is underscore unallowed??? ("0000_0100")

Hi all,

I allways get a compiler error if I try to separate long binary values with underscore!

example:

signal shifreg :: std_logic_vector(15 downto 0);

shiftreg <= "0000_0000_0000_00" & data(1 downto 0);

results in:

"Error (10327): VHDL error at ccd_adc_control.vhd(69): can't determine definition of operator ""&"" -- found 0 possible definitions"

But it isn't the ampersand that is the problem, its the underscore. If you delete it, the compiler is happy.

or another error that says the constant is too long "contains 20 elements instead of 16" (the difference is the count of underscores)

When you look in several VHDL-Books / Documents the underscore allways is described as standard.

Thanks, Thomas

PS: Using Quartus II, 9.1 SP2