how to convert vhdl binary coding to hex code??

There's a few ways you can do this.

1) If your signal is a multiple of 4-bits, then you can use X to indicate hex.

signal d : std_logic_vector(15 downto 0) := X"1234";

2) If your signal is a mixture, you can use a concatenate operator, eg., to set 18-bits to 12345h, you could use

signal d : std_logic_vector(17 downto 0) := "01" & X"2345";

3) Using VHDL-2008 you can use a width specifier

signal d : std_logic_vector(17 downto 0) := 18X"12345";

You can also use conversion functions, eg., to convert an integer value in hex format 16#12345# to std_logic_vector.

Cheers,

Dave

edit - fixed the bus widths for you...