1

我有以下代码：

process(value_counter, hex5_value)
    begin
        if(value_counter <= x"0F") then
            with value_counter select hex4 <=  --error on this line
            "0111111" when x"00", 
            "0000110" when x"01", 
            "1011011" when x"02", 
            "1001111" when x"03", 
            "1100110" when x"04", 
            "1101101" when x"05", 
            "1111101" when x"06", 
            "0000111" when x"07", 
            "1111111" when x"08", 
            "1101111" when x"09",
            "1110111" when x"0A", 
            "1111100" when x"0B",
            "0111001" when x"0C", 
            "1011110" when x"0D",
            "1111001" when x"0E", 
            "1110001" when x"0F";

            hex5<="0111111";
        elsif(value_counter > x"0F") then
            with value_counter mod 10 select hex4 <=
            "0111111" when x"00", 
            "0000110" when x"01", 
            "1011011" when x"02", 
            "1001111" when x"03", 
            "1100110" when x"04", 
            "1101101" when x"05", 
            "1111101" when x"06", 
            "0000111" when x"07", 
            "1111111" when x"08", 
            "1101111" when x"09",
            "1110111" when x"0A", 
            "1111100" when x"0B",
            "0111001" when x"0C", 
            "1011110" when x"0D",
            "1111001" when x"0E", 
            "1110001" when x"0F";

            with hex5_value select hex5 <=
            "0111111" when x"00", 
            "0000110" when x"01", 
            "1011011" when x"02", 
            "1001111" when x"03",
            "1100110" when x"04", 
            "1101101" when x"05", 
            "1111101" when x"06", 
            "0000111" when x"07", 
            "1111111" when x"08", 
            "1101111" when x"09",
            "1110111" when x"0A", 
            "1111100" when x"0B",
            "0111001" when x"0C", 
            "1011110" when x"0D",
            "1111001" when x"0E", 
            "1110001" when x"0F";
        end if;
end process;

但我在运行它时在指示的行上收到以下错误：Error (10500): VHDL syntax error at xxx near text "with"; expecting "end", or "(", or an identifier ("with" is a reserved keyword), or a sequential statement. 任何人都知道是什么原因造成的，以及我如何合法且等效地重写它？

4

2 回答 2

2

“正确”答案是进程内的 CASE 语句或组合区域（即进程外）中的“with ... select”。

但是，如果您创建了一个包含 16 个 7 段显示值的常量数组，并简单地为该数组编制索引，您将拥有更好的 VHDL：

subtype seven_seg is std_logic_vector(6 downto 0);

constant decode : array 0 to 15 of seven_seg := (
            "0111111", "0000110", "1011011", "1001111", 
            "1100110", "1101101", "1111101", "0000111", 
            "1111111", "1101111", "1110111", "1111100",
            "0111001", "1011110", "1111001", "1110001");

    process(value_counter, hex5_value)
        begin
            if value_counter <= x"0F" then
                hex4 <= decode(to_integer(value_counter(3 downto 0)));
                hex5 <= decode(0);
            -- elsif value_counter > x"0F" then  
            -- surely this "elsif" is unnecessary!
            else 
                hex4 <= decode(to_integer(value_counter(7 downto 4)));
                hex5 <= decode(to_integer(hex5_value(3 downto 0)));
            end if;
    end process;
于 2013-01-25T15:09:24.453 回答
0

带有 'with' 的信号赋值是一个并发语句。所以它在进程内无效。一个“案例”可以做到。但是当情况变得安静时，请检查时序分析的结果。

有关更多语法信息，请参阅此链接。

于 2013-01-25T14:44:10.883 回答