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<title>VHDL LRM- Introduction</title>
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<h1><a name="13">Section 13</a></h1>
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<h1>Lexical elements</h1>
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<p>The text of a description consists of one or more design files. The text of a design file is a sequence of lexical elements, each composed of characters; the rules of composition are given in this section.
<h2><a name="13.1"> <a href = "1076_13.HTM#13.1"> 13.1 </a> Character set</a></h2>
<p>The only characters allowed in the text of a VHDL description are the graphic characters and format effectors. Each graphic character corresponds to a unique code of the ISO eight-bit coded character set [(ISO 8859-1 : 1987 (E)], and is represented (visually) by a graphical symbol.
<pre> basic_graphic_character ::=
upper_case_letter | digit | special_character |space_character
graphic_character ::=
basic_graphic_character | lower_case_letter | other_special_character
basic_character ::=
basic_graphic_character | format_effector
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<p>The basic character set is sufficient for writing any description. The characters included in each of the categories of basic graphic characters are defined as follows:
<ol type="a">
<li><code>Uppercase letters<br>A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ?? 快捷鍵說明
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