VHDL：类型为；变量"；与类型不兼容<=

能解释一下为什么我在这段代码中出现语法错误吗

An <= "1110" when anode = "00" else
AN <= "1101" when anode = "01" else
An <= "1011" when anode = "10" else 
An <= "0111" when anode = "11";

segment <= counter_1r    when anode = "00" else
segment <= counter_10r   when anode = "01" else
segment <= counter_100r  when anode = "10" else
segment <= counter_1000r When anode = "11";

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要了解为什么会出现错误消息，请按如下方式查看代码：

An <= "1110" when anode = "00" else (AN <= "1101")....

---

条件信号分配（进程外）写为：

An <=
    "1110" when anode = "00" else
    "1101" when anode = "01" else
    "1011" when anode = "10" else 
    "0111" when anode = "11" else
    "0000";

segment <=
    counter_1r    when anode = "00" else
    counter_10r   when anode = "01" else
    counter_100r  when anode = "10" else
    counter_1000r When anode = "11" else
    "00000000";

---

An您希望这些代码片段做什么？Segment=counter_1r和An=“1101”当阳极=“00”时。。等等……比较还是分配？信号分配是<代码>当阳极具有特定值时，我将分配段和特定值。在过去几天里，我看到你问了几个问题，你给我的印象是，你可以更多地接触一些权威描述VHDL语言的内容。你可以试试宾夕法尼亚大学，它给出了一些例子，而不用关注描述VHDL的语言。
An <= "1110" when anode = "00" else (AN <= "1101")....

An <= "1110" when anode = "00" else
      "1101" when anode = "01" else
      "1011" when anode = "10" else    
      "0111" when anode = "11" else
      null;

An <=
    "1110" when anode = "00" else
    "1101" when anode = "01" else
    "1011" when anode = "10" else 
    "0111" when anode = "11" else
    "0000";

segment <=
    counter_1r    when anode = "00" else
    counter_10r   when anode = "01" else
    counter_100r  when anode = "10" else
    counter_1000r When anode = "11" else
    "00000000";