entity address_decoder is
PORT(address : in STD_LOGIC_VECTOR ( 0 to 3 );
decoded_address : out integer range 0 to 15);
end address_decoder;
architecture dataflow of address_decoder is
begin
PROCESS(address)
begin
if address = "0000" then decoded_address <= '0';
elsif address = "0001" then decoded_address <= '1';
elsif address = "0010" then decoded_address <= '2';
elsif address = "0011" then decoded_address <= '3';
elsif address = "0100" then decoded_address <= '4';
这是即将发生的错误
错误：HDLParsers：800 decode_address类型与＆＃39; 0＆＃39;的类型不兼容。 错误：HDLParsers：800 decode_address类型与＆＃39; 1＆＃39;的类型不兼容。 错误：HDLParsers：800 decode_address类型与＆＃39; 2＆＃39;的类型不兼容。 错误：HDLParsers：800 decode_address类型与＆＃39; 3＆＃39;的类型不兼容。 错误：HDLParsers：800类型的decoding_address与＆＃39; 4＆＃39;的类型不兼容。
是因为address和decoding_address是两种不同的数据类型吗？关于如何摆脱这个错误的任何想法？
答案 0 :(得分：1)
提供此答案是因为Stackoverflow上其他7次出现的ERROR:HDLParsers:800不涉及分配给整数类型的文字，而Morten认为对该问题的实际答案可能很有价值。与答案最接近的匹配问题（参见VHDL: Type of “variable” is incompatible with type of <=）涉及具有位串字面值的整数赋值目标。）
在这个if语句中（缺少并结束if）：
if address = "0000" then decoded_address <= '0';
elsif address = "0001" then decoded_address <= '1';
elsif address = "0010" then decoded_address <= '2';
elsif address = "0011" then decoded_address <= '3';
elsif address = "0100" then decoded_address <= '4';
显示的if语句部分应如下所示：
if address = "0000" then decoded_address <= 0;
elsif address = "0001" then decoded_address <= 1;
elsif address = "0010" then decoded_address <= 2;
elsif address = "0011" then decoded_address <= 3;
elsif address = "0100" then decoded_address <= 4;
decode_address之间存在类型不匹配，它被声明为约束整数，范围为0到15，字符文字为'0'，'1'，'2'，'3'和'4'。
更正后的if语句端口将数字文字（与类型整数兼容）分配给decoding_address。请注意，所有五个值都在decode_address的范围约束内。
答案 1 :(得分：0)
除了@David Koontz回答，你可以使用case语句代替。
case address is
when "0000" => decoded_address <= 0;
when "0001" => decoded_address <= 1;
when "0010" => decoded_address <= 2;
when "0011" => decoded_address <= 3;
when others => decoded_address <= 4;
end case;
并且永远不会忘记涵盖所有条件。
decoded_address <= to_integer(unsigned(address));
当然你需要添加
use ieee.numeric_std.all