将16进制转化为std_logic.txt

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VHDL: Converting a Hexadecimal Value to a Standard Logic Vector

This example shows how to convert a hexadecimal value to a std_logic_vector. 
It is shown in both VHDL '87 (IEEE Std 1076-1987) and VHDL '93 (IEEE Std 1076-1993). 
For more information on using this example in your project, go to: http://www.fpga.com.cn


hex.vhd 

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
USE ieee.std_logic_arith.ALL;

ENTITY hex IS
    PORT(
        D : OUT STD_LOGIC_VECTOR(7 DOWNTO 0));
END hex;

ARCHITECTURE a OF hex IS
BEGIN
-- The following line will convert the hex value 
-- to a STD_LOGIC_VECTOR in VHDL '87.

    D(7 DOWNTO 0) <= to_stdlogicvector(x"FC");
    
-- The following line will work in VHDL '93 (the standard allows 
-- this conversion implicitly).
-- D <= x"FC";
END a;