分别用IF-THEN语句、WHEN-ELSE和CASE语句的表达方式写出4选1多路选择器的VHDL程序
时间: 2024-10-23 21:06:16 浏览: 15
在VHDL(Verilog Hardware Description Language)中,用于实现4选1多路选择器的结构可以根据不同的控制条件有不同的语法。这里分别给出IF-THEN语句、WHEN-ELSE以及CASE语句的示例:
1. **IF-THEN语句**:
```vhdl
signal sel : integer := 0; -- 选择信号,范围0到3
entity FourWaySelector is
Port ( Data : in std_logic_vector(7 downto 0); -- 输入数据
Output : out std_logic_vector(7 downto 0)); -- 输出结果
end entity;
architecture Behavioral of FourWaySelector is
begin
Process(Data, sel)
variable output : std_logic_vector(7 downto 0);
begin
if sel = 0 then
output <= Data(0 downto 0);
elsif sel = 1 then
output <= Data(1 downto 1);
elsif sel = 2 then
output <= Data(2 downto 2);
else -- sel = 3
output <= Data(3 downto 3);
end if;
Output <= output;
end process;
end architecture;
```
2. **WHEN-ELSE语句**:
```vhdl
entity FourWaySelector is
...
component SelectLogic is
Port (sel : in integer; data : in std_logic_vector(7 downto 0); result : out std_logic_vector(7 downto 0));
end component;
...
architecture Behavioral of FourWaySelector is
signal select_logic : SelectLogic;
begin
for i in 0 to 3 generate
when sel = i loop
select_logic sel <= sel;
select_logic data <= Data(i downto i);
Output <= select_logic.result;
end when;
end generate;
end architecture;
```
3. **CASE语句**:
```vhdl
entity FourWaySelector is
...
begin
Process(Data, sel)
variable output : std_logic_vector(7 downto 0);
begin
case sel is
when 0 => output <= Data(0 downto 0);
when 1 => output <= Data(1 downto 1);
when 2 => output <= Data(2 downto 2);
when 3 => output <= Data(3 downto 3);
when others => output <= "00000000"; -- 或者抛出错误处理
end case;
Output <= output;
end process;
end architecture;
```
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