IEEE
IEEE STANDARD VHDL LANGUAGE REFERENCE MANUAL Std 1076-2008
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f) Braces { } enclose a repeated item or items on the right-hand side of a production. The items may
appear zero or more times; the repetitions occur from left to right as with an equivalent left-recursive
rule. Thus, the following two productions are equivalent:
term ::= factor { multiplying_operator factor }
term ::= factor | term multiplying_operator factor
g) If the name of any syntactic category starts with an italicized part, it is equivalent to the category
name without the italicized part. The italicized part is intended to convey some semantic informa-
tion. For example, type_name and subtype_name are both syntactically equivalent to name alone.
h) The term simple_name is used for any occurrence of an identifier that already denotes some
declared entity.
1.3.3 Semantic description
The meaning and restrictions of a particular construct are described with a set of narrative rules immediately
following the syntactic productions. In these rules, an italicized term indicates the definition of that term,
and identifiers appearing entirely in uppercase letters refer to definitions in package STANDARD (see
16.3).
The following terms are used in these semantic descriptions with the following meanings:
erroneous: The condition described represents an ill-formed description; however, implementations are not
required to detect and report this condition. Conditions are deemed erroneous only when it is impossible in
general to detect the condition during the processing of the language.
error: The condition described represents an ill-formed description; implementations are required to detect
the condition and report an error to the user of the tool.
illegal: A synonym for “error.”
legal: The condition described represents a well-formed description.
1.3.4 Front matter, examples, notes, references, and annexes
Prior to this subclause are several pieces of introductory material; following Clause 24 are some annexes and
an index. The front matter, annexes (except Annex B), and index serve to orient and otherwise aid the user
of this standard, but are not part of the definition of VHDL; Annex B, however, is normative.
Some clauses of this standard contain examples, notes, and cross-references to other clauses of the standard;
these parts always appear at the end of a clause. Examples are meant to illustrate the possible forms of the
construct described. Illegal examples are italicized. Notes are meant to emphasize consequences of the rules
described in the clause or elsewhere. In order to distinguish notes from the other narrative portions of this
standard, notes are set as enumerated paragraphs in a font smaller than the rest of the text. Cross-references
are meant to guide the user to other relevant clauses of the standard. Examples, notes, and cross-references
are not part of the definition of the language.
1.3.5 Incorporation of Property Specification Language
VHDL incorporates the simple subset of the Property Specification Language (PSL) as an embedded
language for formal specification of the behavior of a VHDL description. PSL is defined by
IEEE Std 1850
TM
-2005.
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All PSL constructs that appear in a VHDL description shall conform to the
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Information on references can be found in Clause 2.
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