求高手修改一下EDA的课程设计数字秒表；控制模块出了问题LIBRARYIEEE;USEIEEE.STDLOGIC1164.ALL;USEIEEE.STDLOGICUNSIGNED.ALL;ENTITYCTRLISPORT(CLR,CLK,SP:INSTDLOGIC;EN:OUTSTDLOGIC);END;ARCHITECTUREBEHAVEOFCTRLISCO

Question

求高手修改一下EDA的课程设计 数字秒表；控制模块出了问题
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
ENTITY CTRL IS
PORT(CLR,CLK,SP:IN STD_LOGIC;
EN :OUT STD_LOGIC);
END;
ARCHITECTURE BEHAVE OF CTRL IS
CONSTANT S0 :STD_LOGIC_VECTOR(1 DOWNTO 0) := "00";
CONSTANT S1 :STD_LOGIC_VECTOR(1 DOWNTO 0) := "01";
CONSTANT S2 :STD_LOGIC_VECTOR(1 DOWNTO 0) := "11";
CONSTANT S3 :STD_LOGIC_VECTOR(1 DOWNTO 0) := "10";
TYPE STATES IS (S0,S1,S2,S3);
SIGNAL CURRENT_STATE,NEXT_STATE:STATES;
BEGIN
错误提示在倒数第3行，Error (10465):VHDL error at CTRL.vhd(13):name "S0" cannot be used because it is already used for a previously declared item
Error (10465):VHDL error at CTRL.vhd(13):name "S1" cannot be used because it is already used for a previously declared item
下周5要交了，我已经弄了一周了，还是没改成功，

Answer 1

s0已经被用过了 给它起个别的名字 ss0