以下是一个计数器程序，C7,..C0为变量，第二个进程中把该计数好值在时钟锁存脉冲STROBE下，锁存到Q7..Q0中，
程序如下：
library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity corna is
port(clr,clk,door:in std_logic;
strobe:in std_logic;
q7,q6,q5,q4,q3,q2,q1,q0:out std_logic_vector(3 downto 0));
end corna;
architecture behav of corna is
begin
process(door,clk)
variable c0,c1,c2,c3,c4,c5,c6,c7:std_logic_vector(3 downto 0);
begin
if clk'event and clk='1' then
if door='1' and clr='0' then --door=1,clr='0'计数
if c0<"1001" then --c0<9,加1计数
c0:=c0+1;
else
c0:="0000";
if c1<"1001" then --c1<9,加1计数
c1:=c1+1;
else
c1:="0000";
if c2<"1001" then --c2<9,加1计数
c2:=c2+1;
else
c2:="0000";
if c3<"1001" then --c3<9,加1计数
c3:=c3+1;
else
c3:="0000";
if c4<"1001" then --c4<9,加1计数
c4:=c4+1;
else
c4:="0000";
if c5<"1001" then --c5<9,加1计数
c5:=c5+1;
else
c5:="0000";
if c6<"1001" then --c6<9,加1计数
c6:=c6+1;
else
c6:="0000";
if c7<"1001" then --c7<9,加1计数
c7:=c7+1;
else
c7:="0000";
--alm<='1'; --超量程报警
end if;
end if;
end if;
end if;
end if;
end if;
end if;
end if;
else ---clr='1',清0
c7:="0000";
c6:="0000";
c5:="0000";
c4:="0000";
c3:="0000";
c2:="0000";
c1:="0000";
c0:="0000";
end if;
end if;
end process;
process(strobe,c7,c6,c5,c4,c3,c2,c1,c0)
begin
if strobe'event and strobe='1' then
q7<=c7;
q6<=c6;
q5<=c5;
q4<=c4;
q3<=c3;
q2<=c2;
q1<=c1;
q0<=c0;
end if;
end if;
end process;
end behav;
错误如下：identifier"c7" has not been declared....
如何定义C7...C0?
谢谢
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