FAQ part 4 of 4, VHDL glossary 
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 FAQ part 4 of 4, VHDL glossary

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<H1>comp.lang.vhdl<p>Frequently Asked Questions And Answers: Part 4</H1>
<hr>
<strong>Preliminary Remarks</strong><p>
<em>
<P> This part of the FAQ is reprinted from IEEE Std 1076-1993 IEEE
Standard VHDL Language Reference Manual, Copyright &copy; 1994 by the
Institute of Electrical and Electronics Engineers, Inc. The IEEE
disclaims any responsibility or liability resulting from the placement and
use in this product. Information is reprinted with the permission of
the IEEE. Further distribution is not permitted without consent of the
IEEE Standards Department.
</em>
<p>
This is a monthly posting to comp.lang.vhdl containing a VHDL glossary.
Please send additional information directly to the editor:

<P>Corrections and suggestions are appreciated.
Thanks for all corrections.

<p>
This part of the FAQ is posted in html format. Store the text to your local
disk and use a html browser to display the file.

<p>
There are three other regular postings:
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<p>
The following text is reprinted from the Annex B of the IEEE Std 1076-1993
IEEE Standard VHDL Language Reference Manual. Text added by the editor of
the FAQ is enclosed in square brackets "[]". Note, the html links and the
examples are not part of the original IEEE document.<br>
 Once again: if you find any errors
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<hr>
<H2>VHDL Glossary</H1>

<P> This glossary contains brief, informal descriptions for a number
of terms and phrases used to define this language. The
complete, formal definition
of each term or phrase is provided in the main body of the
standard.<P>

For each entry, the relevant clause numbers [(of the VHDL Language Reference
Manual)] in the text are given. Some descriptions refer to multiple clauses
in which the single concept is discussed; for these, the clause number
containing the definition of the concept is given in italics. Other descriptions
contain multiple clause numbers when they refer to multiple concepts;
for these, none of the clause numbers are italicized.<P>

<B>B.1 <A NAME="abstract literal"> abstract literal</A>:</B> A <A
HREF="#literal">literal</A> of the <A
HREF="#universal_real">universal_real</A> abstract <A
HREF="#type">type</A> or the <A
HREF="#universal_integer">universal_integer</A> abstract <A
HREF="#type">type</A>. (&#167;13.2, &#167;13.4)<P>

<B>B.2 <A NAME="access type"> access type</A>:</B> A <A
HREF="#type">type</A> that provides access to an <A
HREF="#object">object</A> of a given <A HREF="#type">type</A>. Access
to such an <A HREF="#object">object</A> is achieved by an <A
HREF="#access value">access value</A> returned by an <A
HREF="#allocator">allocator</A>; the <A HREF="#access value">access
value</A> is said to <A HREF="#designate">designate</A> the <A
HREF="#object">object</A>. (&#167;3, &#167;13.3)<P>

<A HREF="#Example1">[Example E.1]</A>

<p>

<B>B.3 <A NAME="access mode"> access mode</A>:</B> The
mode in which a file <A HREF="#object">object</A> is
opened, which can be either read-only or write-only. The
access mode depends on the value supplied to
the Open_Kind <A HREF="#parameter">parameter</A>. (&#167;3.4.1,
&#167;14.3).<P>

<B>B.4 <A NAME="access value"> access value</A>:</B> A value of an <A
HREF="#access type">access type</A>. This value is returned by an <A
HREF="#allocator">allocator</A> and <A
HREF="#designate">designates</A> an <A HREF="#object">object</A>
(which must be a <A HREF="#variable">variable</A>) of a given <A
HREF="#type">type</A>. A null access value
<A HREF="#designate">designates</A> no <A
HREF="#object">object</A>. An access value
can only <A HREF="#designate">designate</A> an <A
HREF="#object">object</A> created by an <A
HREF="#allocator">allocator</A>; it cannot <A
HREF="#designate">designate</A> an <A HREF="#object">object</A>
declared by an <A HREF="#object">object</A> <A
HREF="#declaration">declaration</A>. (&#167;3, 3.3)<P>

<A HREF="#Example1">[Example E.1]</A>

<p>

<B>B.5 <A NAME="active driver"> active driver</A>:</B> A <A
HREF="#driver">driver</A> that acquires a new value during a <A
HREF="#simulation cycle">simulation cycle</A> regardless of whether
the new value is different from the previous value. (&#167;12.6.2,
&#167;12.6.4)<P>

<B>B.6 <A NAME="actual"> actual</A>:</B> An <A
HREF="#expression">expression</A>, a <A HREF="#port">port</A>, a <A
HREF="#signal">signal</A>, or a <A HREF="#variable">variable</A>
associated with a <A HREF="#formal">formal port</A>,
<A HREF="#formal">formal parameter</A>, or
<A HREF="#formal">formal generic</A>. (&#167;1.1.1.1, &#167;1.1.1.2,
&#167;3.2.1.1, &#167;4.3.1.2, &#167;4.3.2.2, &#167;5.2.1,
&#167;5.2.1.2)<P>

<B>B.7 <A NAME="aggregate"> aggregate</A>:</B><P>

<OL> <li>The kind of <A HREF="#expression">expression</A>, denoting a
value of a <A HREF="#composite type">composite type</A>. The value is
specified by giving the value of each of the elements of the <A
HREF="#composite type">composite type</A>. Either a <A
HREF="#positional association">positional association</A> or a <A
HREF="#named association">named association</A> may be used to
indicate which value is associated with which element.</li> <li>A kind
of target of a <A HREF="#variable">variable</A> assignment statement
or <A HREF="#signal">signal</A> assignment statement assigning a
composite value. The target is then said to <I>be in the form of an
aggregate</I>. (&#167;7.3.1, &#167;7.3.2,
&#167;7.3.4, 7.3.5, &#167;7.5.2)</li> </OL><P>

<A HREF="#Example2">[Example E.2]</A>

<p>

<B>B.8 <A NAME="alias"> alias</A>:</B> An alternate <A
HREF="#name">name</A> for a <A HREF="#named entity">named
entity</A>. (&#167;4.3.3)<P>

<B>B.9 <A NAME="allocator"> allocator</A>:</B> An operation used to
create <A HREF="#anonymous">anonymous</A>, <A
HREF="#variable">variable objects</A> accessible
by means of <A HREF="#access value">access values</A>. (&#167;3.3,
&#167;7.3.6)<P>

<B>B.10 <A NAME="analysis"> analysis</A>:</B> The syntactic and
semantic analysis of source code in a VHDL <A HREF="#design file">design
file</A> and the insertion of intermediate form representations of <A
HREF="#design unit">design units</A> into a <A HREF="#design library">
design library</A>. (&#167;1 1.1, &#167;11.2, &#167;11.4)<P>

<B>B.11 <A NAME="anonymous"> anonymous</A>:</B> The undefined <A
HREF="#simple name">simple name</A> of an item, which is created
implicitly. The base <A HREF="#type">type</A> of a
<A HREF="#numeric type">numeric type</A> or an <A HREF="#array type">
array type</A> is <A HREF="#anonymous">anonymous</A>; similarly, the <A
HREF="#object">object</A> denoted by an <A HREF="#access value">access
value</A> is <A HREF="#anonymous">anonymous</A>. (&#167;4.1)<P>

<B>B.12 <A NAME="appropriate"> appropriate</A>:</B> A prefix is said
to be appropriate for a <A
HREF="#type">type</A> if the <A HREF="#type">type</A> of the prefix is
the <A HREF="#type">type</A> considered, or if the <A
HREF="#type">type</A> of the prefix is an <A HREF="#access type">
access type</A> whose <A HREF="#designated type">designated
type</A> is the <A HREF="#type">type</A> considered. (&#167;6.1)<P>

<B>B.13 <A NAME="architecture body"> architecture body</A>:</B> A body
associated with an <A HREF="#entity declaration">entity
declaration</A> to describe the internal organization or operation of
a <A HREF="#design entity">design entity</A>. An <A
HREF="#architecture body">architecture body</A> is used to describe
the behavior, data flow, or structure of a <A HREF="#design entity">
design entity</A>. (&#167;1, &#167;1.2)<P>

<B>B.14 <A NAME="array object"> array object</A>:</B> An <A
HREF="#object">object</A> of an <A HREF="#array type">array
type</A>. (&#167;3)<P>

<A HREF="#Example3">[Example E.3]</A>

<p>

<B>B.15 <A NAME="array type"> array type</A>:</B> A <A
HREF="#type">type</A>, the value of which consists of elements that
are all of the same <A HREF="#subtype">subtype</A> (and hence, of the
same <A HREF="#type">type</A>). Each element is uniquely distinguished
by an index (for a one-dimensional array) or by a sequence of indexes
(for a multidimensional array). Each index must be a value of a <A
HREF="#discrete type">discrete type</A> and must lie in the correct <A
HREF="#index range">index range</A>. (&#167;3.2.1)<P>

<A HREF="#Example3">[Example E.3]</A>

<p>

<B>B.16 <A NAME="ascending range"> ascending range</A>:</B> A <A
HREF="#range">range</A> L <B>to</B> R. (&#167;3.1)<P>

<B>B.17 <A NAME="ASCII"> ASCII</A>:</B> The American Standard Code for
Information Interchange. The package Standard contains the definition
of the <A HREF="#type">type</A> Character, the first 128 values of
which represent the ASCII character
set. (&#167;3.1.1, &#167;14.2)<P>

<B>B.18 <A NAME="assertion violation"> assertion violation</A>:</B> A
violation that occurs when the condition of an assertion statement
evaluates to false. (&#167;8.2)<P>

<A HREF="#Example4">[Example E.4]</A>

<p>

<B>B.19 <A NAME="associated driver"> associated driver</A>:</B> The
single <A HREF="#driver">driver</A> for a <A HREF="#signal">signal</A>
in the (explicit or equivalent) process statement containing the <A
HREF="#signal">signal</A> assignment statement. (&#167;12.6.1)<P>

<B>B.20 <A NAME="associated in whole"> associated in whole</A>:</B>
When a single <A HREF="#association element">association element</A>
of a composite <A HREF="#formal">formal</A> supplies the association
for the entire <A HREF="#formal">formal</A>. (&#167;4.3.2.2)<P>

<B>B.21 <A NAME="associated individually"> associated
individually</A>:</B> A property of a <A HREF="#formal">formal port,
generic, or parameter</A> of a <A HREF="#composite type">
composite type</A> with respect to some <A HREF="#association list">
association list</A>. A composite <A HREF="#formal">formal</A>
whose association is defined by multiple
<A HREF="#association element">
association elements</A> in a single <A HREF="#association
list">association list</A> is said to be <I>associated individually</I> in
that list. The formats of such <A HREF="#association element">
association elements</A> must denote
non-overlapping <A HREF="#subelement">subelements</A> or <A
HREF="#slice">slices</A> of the <A
HREF="#formal">formal</A>. (&#167;4.3.2.2)<P>

<B>B.22 <A NAME="association element"> association element</A>:</B> An
element that associates an <A HREF="#actual">actual</A> or local with
a local or <A HREF="#formal">formal</A>. (&#167;4.3.2.2)<P>

<B>B.23 <A NAME="association list"> association list</A>:</B> A list
that establishes correspondences between <A HREF="#formal">formal</A>
or <A HREF="#local port">local port</A> or <A
HREF="#parameter">parameter</A> <A HREF="#name">names</A> and local or
<A HREF="#actual">actual</A> <A HREF="#name">names</A> or <A
HREF="#expression">expressions</A>. (&#167;4.3.2.2)<P>

<B>B.24 <A NAME="attribute"> attribute</A>:</B> A definition of some
characteristic of a <A HREF="#named entity">named entity</A>. Some
attributes are predefined for <A HREF="#type">types</A>,
<A HREF="#range">ranges</A>, values, <A HREF="#signal">signals</A>,
and functions. The remaining attributes are user defined and are always
<A HREF="#constant">constants</A>. (&#167;4.4)<P>

<A HREF="#Example5">[Example E.5]</A>

<p>

<B>B.25 <A NAME="base specifier"> base specifier</A>:</B> A lexical
element that indicates whether a <A HREF="#bit string literal">bit
string literal</A> is to be interpreted as a binary, octal, or
hexadecimal value. (&#167;13.7)<P>

<B>B.26 <A NAME="base type">base type</A>:</B> The <A
HREF="#type">type</A> from which a <A HREF="#subtype">subtype</A>
defines a subset of possible values, otherwise known as a <A
HREF="#constraint">constraint</A>. This subset is not required to be
proper. The base <A HREF="#type">type</A> of a <A
HREF="#type">type</A> is the <A HREF="#type">type</A> itself. The base
<A HREF="#type">type</A> of a <A HREF="#subtype">subtype</A> is found
by recursively examining the <A HREF="#type">type</A> mark in the <A
HREF="#subtype">subtype</A> indication defining the <A
HREF="#subtype">subtype</A>. If the <A HREF="#type">type</A> mark
denotes a <A HREF="#type">type</A>, that <A
HREF="#type">type</A> is the base <A HREF="#type">type</A> of the <A
HREF="#subtype">subtype</A>; otherwise, the <A HREF="#type">type</A>
mark is a <A HREF="#subtype">subtype</A>, and this procedure is
repeated on that <A HREF="#subtype">subtype</A>. (&#167;3) <I>See also</I> <A
HREF="#subtype"> subtype</A>.<P>

<A HREF="#Example6">[Example E.6]</A>

<p>

<B>B.27 <A NAME="based literal"> based literal</A>:</B> An <A
HREF="#abstract literal">abstract literal</A> expressed in a form that
specifies the base explicitly. The base is restricted to the range
2 to 16. (&#167;13.4.2)<P>

<B>B.28 <A NAME="basic operation"> basic operation</A>:</B> An
operation that is inherent in one of the following:<P>

<ol> <li>An assignment (in an assignment statement or
initialization);</li> <li>An <A HREF="#allocator">allocator</A>;</li>
<li>A <A HREF="#selected name">selected name</A>, an indexed <A
HREF="#name">name</A>. or a <A HREF="#slice">slice</A> <A
HREF="#name">name</A>;</li> <li>A qualification (in a qualified <A
HREF="#expression">expression</A>), an explicit
<A HREF="#type conversion">type conversion</A>, a <A HREF="#formal">formal</A> or <A
HREF="#actual">actual</A> <A HREF="#designator">designator</A> in the
form of a <A HREF="#type conversion">type conversion</A>, or an
implicit <A HREF="#type conversion">type conversion</A> of a value of
<A HREF="#type">type</A> <A
HREF="#universal_integer">universal_integer</A> or <A
HREF="#universal_real">universal_real</A> to the corresponding value
of another <A HREF="#numeric type">numeric type</A>; or</li> <li>A <A
HREF="#numeric literal">numeric literal</A> (for a universal <A
HREF="#type">type</A>), the <A HREF="#literal">literal</A> null (for
an <A HREF="#access type">access type</A>), a
<A HREF="#string literal">string literal</A>, a
<A HREF="#bit string literal">bit
string literal</A>, an <A HREF="#aggregate">aggregate</A>, or a
predefined <A HREF="#attribute">attribute</A>. (&#167;3)</li> </ol><P>

<B>B.29 <A NAME="basic signal"> basic signal</A>:</B> A <A
HREF="#signal">signal</A> that determines the
<A HREF="#driving value">driving values</A> for all other <A
HREF="#signal">signals</A>. A <A HREF="#basic signal">basic signal</A>
is<P>

<ul> <li>Either a scalar <A HREF="#signal">signal</A> or a <A
HREF="#resolved signal">resolved signal</A>;</li> <li>Not a <A
HREF="#subelement">subelement</A> of a <A HREF="#resolved signal">
resolved signal</A>;</li> <li>Not an
<A HREF="#implicit signal">implicit signal</A> of the form
<A HREF="#attribute">S&#39;Stable(T), S&#39;Quiet(T), or
S&#39;Transaction</A>; and</li> <li>Not an <A HREF="#guard">implicit
signal GUARD</A>. (&#167;12.6.2)</li> </ul><P>

<B>B.30 <A NAME="belong (to a range)"> belong (to a range)</A>:</B> A
property of a value with respect to some <A
HREF="#range">range</A>. The value V is said to <I>belong to a range</I>
if the relations (<A HREF="#lower bound">
lower bound</A> &lt;= V) and (V &lt;= <A HREF="#upper bound">
upper bound</A>) are both true, where <A HREF="#lower bound">
lower bound</A> and <A HREF="#upper bound">upper bound</A> are
the lower and <A HREF="#upper bound">upper bounds</A>, respectively,
of the <A HREF="#range">range</A>. (&#167;3.1, &#167;3.2.1)<P>

<B>B.31 <A NAME="belong (to a subtype)"> belong (to a
subtype)</A>:</B> A property of a value with respect to some <A
HREF="#subtype">subtype</A>. A value is said to <I>belong to a subtype</I>
of a given <A HREF="#type">type</A>
if it belongs to the <A HREF="#type">type</A> and satisfies the
applicable <A HREF="#constraint">constraint</A>. (&#167;3,
&#167;3.2.1)<P>

<B>B.32 <A NAME="binding"> binding</A>:</B> The process of associating
a <A HREF="#design entity">design entity</A> and, optionally, an
architecture with an <A HREF="#instance">instance</A> of a
component. A <A HREF="#binding">binding</A> can be specified in an
explicit or a default <A HREF="#binding">binding</A>
indication. (&#167;1.3, &#167;5.2.1, &#167;5.2.2, &#167;12.3.2.2,
&#167;12.4.3)<P>

<B>B.33 <A NAME="bit string literal"> bit string literal</A>:</B> A <A
HREF="#literal">literal</A> formed by a sequence of
<A HREF="#extended digit">extended digits</A> enclosed between two
quotation (&quot;)
characters and preceded by a <A HREF="#base specifier">base
specifier</A>. The <A HREF="#type">type</A> of a
<A HREF="#bit string literal">bit string literal</A> is determined from the
context. (&#167;7.3.1, &#167;13.7)<P>

<A HREF="#Example7">[Example E.7]</A>

<p>

<B>B.34 <A NAME="block"> block</A>:</B> The representation of a
portion of the hierarchy of a design. A <A HREF="#block">block</A> is
either an <A HREF="#external block">external block</A> or an <A
HREF="#internal block">internal block</A>. (&#167;1, &#167;1.1.1.1,
&#167;1.1.1.2, &#167;1.2.1, &#167;1.3, &#167;1.3.1, &#167;1.3.2)<P>

<A HREF="#Example8">[Example E.8]</A>

<p>

<B>B.35 <A NAME="bound"> bound</A>:</B> A label that is identified in
the instantiation list of a <A HREF="#configuration">configuration</A>
<A HREF="#specification">specification</A>. (&#167;5.2)<P>

<B>B.36 <A NAME="box"> box</A>:</B> The symbol &lt;&gt; in an <A
HREF="#index subtype">index subtype</A> definition, which stands for
an undefined <A HREF="#range">range</A>. Different <A
HREF="#object">objects</A> of the <A HREF="#type">type</A> need not
have the same bounds and direction. (&#167;3.2.1)<P>

<B>B.37 <A NAME="bus"> bus</A>:</B> One kind of
<A HREF="#guarded signal">guarded signal</A>. A bus
floats to a user-specified value when all of its <A HREF="#driver">
drivers</A> are turned off. (&#167;4.3.1.2, &#167;4.3.2)<P>

<B>B.38 <A NAME="character literal"> character literal</A>:</B> A <A
HREF="#literal">literal</A> of the <A HREF="#character type">character
type</A>. Character literals are
formed by enclosing one of the graphic characters (including the space
and nonbreaking space characters) between two apostrophe (&#39;)
characters. (&#167;13.2, &#167;13.5)<P>

<B>B.39 <A NAME="character type"> character type</A>:</B> An <A
HREF="#enumeration type">enumeration type</A> with at least one <A
HREF="#character literal">character literal</A> among its <A
HREF="#enumeration literal">enumeration literals</A>. (&#167;3.1.1,
&#167;3.1.1.1)<P>

<B>B.40 <A NAME="closely related types"> closely related types:</B>
Two <A HREF="#type">type</A> marks that denote
the same <A HREF="#type">type</A> or two <A HREF="#numeric type">
numeric types</A>. Two <A HREF="#array type">array types</A> may
also be closely related if they have the same dimensionality, if their
index <A HREF="#type">types</A> at each position are closely related,
and if the <A HREF="#array type">array types</A> have the same element
<A HREF="#type">types</A>. Explicit <A HREF="#type conversion">type
conversion</A> is only allowed between closely related types.
(&#167;7.3.5)<P>

<B>B.41 <A NAME="complete"> complete</A>:</B> A loop that has finished
executing. Similarly, an iteration scheme of a loop is
complete when the condition of a while iteration
scheme is FALSE or all of the values of the <A HREF="#discrete range">
discrete range</A> of a for iteration scheme have been assigned
to the iteration parameter. (&#167;8.9)<P>

<B>B.42 <A NAME="complete context"> complete context</A>:</B> A <A
HREF="#declaration">declaration</A>, a <A
HREF="#specification">specification</A>, or a statement;
complete contexts are used in overload
resolution. (&#167;10.5)<P>

<B>B.43 <A NAME="composite type"> composite type</A>:</B> A <A
HREF="#type">type</A> whose values have elements. There are two
classes of composite types: <A
HREF="#array type">array types</A> and <A HREF="#record type">record
types</A>. (&#167;3, &#167;3.2)<P>

<A HREF="#Example3">[Example E.3]</A>

<p>

<B>B.44 <A NAME="concurrent statement"> concurrent statement</A>:</B>
A statement that <A HREF="#execute">executes</A> asynchronously, with
no defined relative order. Concurrent statements are used for
dataflow and structural descriptions. (&#167;9)<P>

<A HREF="#Example9">[Example E.9]</A>

<p>

<B>B.45 <A NAME="configuration"> configuration</A>:</B> A construct
that defines how component <A HREF="#instance">instances</A> in a
given <A HREF="#block">block</A> are <A HREF="#bound">bound</A> to
design entities in order to describe how design entities are put
together to form a complete design. (&#167;1,
&#167;1.3. 5.2)<P>

<B>B.46 <A NAME="conform"> conform</A>:</B> Two
<A HREF="#subprogram specification">subprogram specifications</A>,
are said to conform if, apart from certain
allowed minor
variations, both <A HREF="#specification">specifications</A> are
formed by the same sequence of lexical elements, and corresponding
lexical elements are given the same meaning by the visibility
rules. Conformance is defined similarly for
<A HREF="#deferred constant">deferred constant</A> <A
HREF="#declaration">declarations</A>. (&#167;2.7)<P>

<B>B.47 <A NAME="connected"> connected</A>:</B> A <A
HREF="#formal">formal</A> <A HREF="#port">port</A> associated with an
<A HREF="#actual">actual</A> <A HREF="#port">port</A> or <A
HREF="#signal">signal</A>. A <A HREF="#formal">formal</A> <A
HREF="#port">port</A> associated with the reserved word <B>open</B> is said
to be <I>unconnected</I>. (&#167;1.1.1.2)<P>

<B>B.48 <A NAME="constant"> constant</A>:</B> An <A
HREF="#object">object</A> whose value may not be changed.
Constants may be <I>explicitly</I> declared, <A
HREF="#subelement">subelements</A> of
<A HREF="#explicitly declared constant">explicitly
declared constants</A>, or interface
constants. Constants declared in packages may
also be <A HREF="#deferred constant">deferred
constants</A>. (&#167;4.3.1.1)<P>

<B>B.49 <A NAME="constraint"> constraint</A>:</B> A subset of the
values of a <A HREF="#type">type</A>. The set of possible values for
an <A HREF="#object">object</A> of a given <A HREF="#type">type</A>
that can be subjected to a condition called a <A
HREF="#constraint">constraint</A>. A value is said to <A
HREF="#satisfy">satisfy</A> the constraint
if it satisfies the corresponding condition. There are
<A HREF="#index constraint">index constraints</A>,
<A HREF="#range constraint">range constraints</A>, and size
constraints. (&#167;3)<P>

<B>B.50 <A NAME="conversion function"> conversion function</A>:</B> A
function used to convert values flowing through associations. For
interface <A HREF="#object">objects</A> of <A HREF="#mode">mode</A>
<B>in</B>, conversion functions are
allowed only on <A HREF="#actual">actuals</A>. For interface <A
HREF="#object">objects</A> of <A HREF="#mode">mode</A> <B>out</B> or
<B>buffer</B>, conversion functions are allowed
only on <A HREF="#formal">formals</A>. For interface <A
HREF="#object">objects</A> of <A HREF="#mode">mode</A> <B>inout</B> or
<B>linkage</B>, conversion functions are
allowed on both <A HREF="#formal">formals</A> and <A
HREF="#actual">actuals</A>. Conversion
functions have a single <A HREF="#parameter">parameter</A>. A
conversion function associated with an
<A HREF="#actual">actual</A> accepts the <A HREF="#type">type</A> of
the <A HREF="#actual">actual</A> and returns the <A
HREF="#type">type</A> of the <A HREF="#formal">formal</A>. A
conversion function associated with a
<A HREF="#formal">formal</A> accepts the <A HREF="#type">type</A> of
the <A HREF="#formal">formal</A> and returns the <A
HREF="#type">type</A> of the <A
HREF="#actual">actual</A>. (&#167;4.3.2.2)<P>

<B>B.51 <A NAME="convertible"> convertible</A>:</B> A property of an
operand with respect to some <A HREF="#type">type</A>. An operand is
convertible to some <A
HREF="#type">type</A> if there exists an implicit conversion to that
<A HREF="#type">type</A>. (&#167;7.3.5)<P>

<B>B.52 <A NAME="current value"> current value</A>:</B> The value
component of the single <A HREF="#transaction">transaction</A> of a <A
HREF="#driver">driver</A> whose time component is not greater than the
current simulation time. (&#167;12.6. 12.6.1, &#167;12.6.2,
&#167;12.6.3)<P>

<B>B.53 <A NAME="decimal literal"> decimal literal</A>:</B> An <A
HREF="#abstract literal">abstract literal</A> that is expressed in
decimal notation. The base of the <A HREF="#literal">literal</A> is
implicitly 10. The <A HREF="#literal">literal</A> may optionally
contain an exponent or a decimal point and fractional
part. (&#167;13.4.1)<P>

<B>B.54 <A NAME="declaration"> declaration</A>:</B> A construct that
defines a declared entity and associates an identifier (or some other
notation) with it. This association is in effect within a region of
text that is called the <A HREF="#scope">scope</A> of the
declaration. Within the <A
HREF="#scope">scope</A> of a declaration,
there are places where it is possible to use the identifier to refer
to the associated declared entity; at such places, the identifier
is said to be the <A HREF="#simple name">simple name</A> of the <A
HREF="#named entity">named entity</A>. The <A HREF="#simple name">
simple name</A> is said to <A HREF="#denote">denote</A> the
associated <A HREF="#named entity">named entity</A>. (&#167;4)<P>

<B>B.55 <A NAME="declarative part"> declarative part</A>:</B> A
syntactic component of certain <A HREF="#declaration">declarations</A>
or statements (such as <A HREF="#entity declaration">entity
declarations</A>, <A HREF="#architecture body">architecture
bodies</A>, and <A HREF="#block">block</A>
statements). The <A HREF="#declarative part">declarative part</A>
defines the lexical area (usually introduced by a keyword such as <B>is</B>
and terminated with another keyword such as <B>begin</B>) within which <A
HREF="#declaration">declarations</A> may occur. (&#167;1.1.2,
&#167;1.2.1, &#167;1.3, &#167;2.6, &#167;9.1, &#167;9.2, &#167;9.6.1,
&#167;9.6.2)<P>

<B>B.56 <A NAME="declarative region"> declarative region</A>:</B> A
semantic component of certain <A HREF="#declaration">declarations</A>
or statements. A declarative region
may include disjoint parts, such as the
declarative region of an <A HREF="#entity declaration">
entity declaration</A>, which <A
HREF="#extend">extends</A> to the end of any
<A HREF="#architecture body">architecture body</A> for that entity.
(&#167;10.1)<P>

<B>B.57 <A NAME="decorate"> decorate</A>:</B> To associate a
user-defined <A HREF="#attribute">attribute</A> with a
<A HREF="#named entity">named entity</A> and to {define} the value of
that <A HREF="#attribute">attribute</A>. (&#167;5.1)<P>

<B>B.58 <A NAME="default expression"> default expression</A>:</B> A
default value that is used for a <A HREF="#formal">formal
generic, port, or parameter</A> if the interface <A
HREF="#object">object</A> is unassociated. A
default expression is also
used to provide an initial value for <A HREF="#signal">signals</A>
and their <A HREF="#driver">drivers</A>.
(&#167;4.3.1.2, &#167;4.3.2.2)<P>

<A HREF="#Example10">[Example E.10]</A>

<p>

<B>B.59 <A NAME="deferred constant"> deferred constant</A>:</B> A <A
HREF="#constant">constant</A> that is declared without an assignment
symbol (:=) and <A HREF="#expression">expression</A> in a package <A
HREF="#declaration">declaration</A>. A corresponding
<A HREF="#full declaration">full declaration</A> of the
constant must exist in the package body to define
the value of the constant. (&#167;4.3.1.1)<P>

<A HREF="#Example11">[Example E.11]</A>

<p>

<B>B.60 <A NAME="delta cycle"> delta cycle</A>:</B> A <A
HREF="#simulation cycle">simulation cycle</A> in which the simulation
time at the beginning of the cycle is the same as at the end of the
cycle. That is, simulation time is not advanced in a
<A HREF="#delta cycle">delta cycle</A>. Only nonpostponed
processes can be executed
during a <A HREF="#delta cycle">delta cycle</A>. (&#167;12.6.4)<P>

<B>B.61 <A NAME="denote"> denote</A>:</B> A property of the identifier
given in a <A HREF="#declaration">declaration</A>. Where the <A
HREF="#declaration">declaration</A> is <A HREF="#visible">visible</A>,
the identifier given in the <A HREF="#declaration">declaration</A> is
said to <I>denote</I> the <A HREF="#named entity">named
entity</A> declared in the <A
HREF="#declaration">declaration</A>. (&#167;4)<P>

<B>B.62 <A NAME="depend (on a library unit)"> depend (on a library
unit)</A>:</B> A <A HREF="#design unit">design unit</A> that
explicitly or implicitly mentions other <A HREF="#library unit">
library units</A> in a use clause. These dependencies affect the
allowed order of <A HREF="#analysis">analysis</A> of
<A HREF="#design unit">design units</A>. (&#167;11.4)<P>

<B>B.63 <A NAME="depend (on a signal value)"> depend (on a signal
value)</A>:</B> A property of an <A HREF="#implicit signal">implicit
signal</A> with respect to some other <A
HREF="#signal">signal</A>. The <A HREF="#current value">current
value</A> of an <A HREF="#implicit signal">implicit signal</A> R is
said to <I>depend</I> on the <A HREF="#current value">current value</A> of
another <A HREF="#signal">signal</A> S if R
denotes an <A HREF="#implicit signal">implicit
signal</A> S&#39;Stable(T), S&#39;Quiet(T), or S&#39;Transaction, or if R
denotes an implicit <A HREF="#guard">GUARD signal</A> and S
is any other <A HREF="#implicit signal">implicit signal</A>
named within the <A HREF="#guard expression">guard expression</A>
that defines the <A HREF="#current value">current value</A> of R.
(&#167;12.6.3)<P>

<B>B.64 <A NAME="descending range"> descending range</A>:</B> A <A
HREF="#range">range</A> L <B>downto</B> R. (&#167;3.1)<P>

<B>B.65 <A NAME="design entity"> design entity</A>:</B> An <A
HREF="#entity declaration">entity declaration</A> together with an
associated <A HREF="#architecture body">architecture
body</A>. Different design entities may share the same <A
HREF="#entity declaration">entity declaration</A>, thus describing
different components with the same interface or different views of the
same component. (&#167;1)<P>

<B>B.66 <A NAME="design file"> design file</A>:</B> One or more <A
HREF="#design unit">design units</A> in sequence. (&#167;1.1)<P>

<B>B.67 <A NAME="design hierarchy"> design hierarchy</A>:</B> The
complete representation of a design that results
from the successive decomposition of a <A HREF="#design entity">design
entity</A> into subcomponents and <A HREF="#binding">binding</A> of
those components to other design entities that may be decomposed in a
similar manner. (&#167;1)<P>

<B>B.68 <A NAME="design library"> design library</A>:</B> A
host-dependent storage facility for intermediate-form representations
of analyzed <A HREF="#design unit">design units</A>. (&#167;11.2)<P>

<B>B.69 <A NAME="design unit"> design unit</A>:</B> A construct that
can be independently analyzed and stored in a
<A HREF="#design library"> design library</A>. A
design unit
may be an <A HREF="#entity declaration">entity declaration</A>, an <A
HREF="#architecture body">architecture body</A>, a <A
HREF="#configuration">configuration declaration</A>, a package
declaration, or a package body declaration. (&#167;11.1)<P>

<B>B.70 <A NAME="designate"> designate</A>:</B> A property of <A
HREF="#access value">access values</A> that relates the value to some
<A HREF="#object">object</A> when the <A HREF="#access value">access
value</A> is nonnull. A nonnull <A HREF="#access value">access
value</A> is said to <I>designate</I> an <A
HREF="#object">object</A>. (&#167;3.3)<P>

<B>B.71 <A NAME="designated subtype"> designated subtype</A>:</B> For
an <A HREF="#access type">access type</A>, the <A
HREF="#subtype">subtype</A> defined by the <A
HREF="#subtype">subtype</A> indication of the
<A HREF="#access type">access type</A> definition. (&#167;3.3)<P>

<B>B.72 <A NAME="designated type"> designated type</A>:</B> For an <A
HREF="#access type">access type</A>, the base <A HREF="#type">type</A>
of the <A HREF="#subtype">subtype</A> defined by the <A
HREF="#subtype">subtype</A> indication of the <A HREF="#access type">
access type</A> definition. (&#167;3.3)<P>

<B>B.73 <A NAME="designator"> designator</A>:</B><P>

<ol>
<li>Syntax that forms part of an <A HREF="#association element">
   association element</A>. A formal designator specifies which <A
   HREF="#formal">formal parameter, port, or generic</A> (or which <A
   HREF="#subelement">subelement</A> or <A HREF="#slice">slice</A> of a
   <A HREF="#parameter">parameter</A>, <A HREF="#port">port</A>, or <A
   HREF="#generic">generic</A>) is to be associated with an <A
   HREF="#actual">actual</A> by the given <A HREF="#association element">
   association element</A>. An actual designator specifies which <A
   HREF="#actual">actual expression, signal, or variable</A> is to
   be associated with a <A HREF="#formal">formal</A> (or <A
   HREF="#subelement">subelement</A> or <A
   HREF="#subelement">subelements</A> of a <A
   HREF="#formal">formal</A>). An actual designator may also
   specify that the <A HREF="#formal">formal</A> in the given
   <A HREF="#association element">association element</A> is
   to be left unassociated (with an actual designator of
   <B>open</B>). (&#167;4.3.2.2)</li>
<li>An identifier,
   <A HREF="#character literal">character literal</A>, or operator
   symbol that defines an <A
   HREF="#alias">alias</A> for some other <A
   HREF="#name">name</A>. (&#167;4.3.3)</li>
<li>A <A HREF="#simple name">simple name</A> that denotes a predefined
   or user-defined <A HREF="#attribute">attribute</A> in an <A
   HREF="#attribute">attribute</A> <A HREF="#name">name</A>, or a
   user-defined <A HREF="#attribute">attribute</A> in an <A
   HREF="#attribute">attribute</A> <A
   HREF="#specification">specification</A>. (&#167;5.1, &#167;6.6)</li>
<li>An <A HREF="#simple name">simple name</A>,
   <A HREF="#character literal">character literal</A>, or operator
   symbol, and possibly a
   signature, that denotes a
   <A HREF="#named entity">named entity</A> in the entity name list of an
   <A HREF="#attribute">attribute</A> <A
   HREF="#specification">specification</A>. (&#167;5.1)</li>
<li>An identifier or operator symbol that defines the <A
   HREF="#name">name</A> of a subprogram. (&#167;2.1)</li> </ol><P>

<B>B.74 <A NAME="directly visible"> directly visible</A>:</B> A <A
HREF="#visible">visible</A> <A HREF="#declaration">declaration</A>
that is not <A HREF="#visible">visible</A> by selection. A <A
HREF="#declaration">declaration</A> is directly visible
within its <A HREF="#immediate scope">immediate scope</A>,
excluding any places where the <A HREF="#declaration">declaration</A>
is <A HREF="#hidden">hidden</A>. A
<A HREF="#declaration">declaration</A> occurring
<A HREF="#immediately within">immediately within</A> the
<A HREF="#visible">visible</A> part
of a package can be made directly visible by means of a use clause.
(&#167;10.3, 10.4). <I>See also</I> <A HREF="#visible"> visible</A>.<P>

<B>B.75 <A NAME="discrete array"> discrete array</A>:</B> A
one-dimensional array whose elements are of a
<A HREF="#discrete type">discrete type</A>. (&#167;7.2.3)<P>

<B>B.76 <A NAME="discrete range"> discrete range</A>:</B> A <A
HREF="#range">range</A> whose <A HREF="#bound">bounds</A> are of a <A
HREF="#discrete type">discrete type</A>. (&#167;3.2.1,
&#167;3.2.1.1)<P>

<B>B.77 <A NAME="discrete type"> discrete type</A>:</B> An <A
HREF="#enumeration type">enumeration type</A> or an
<A HREF="#integer type">integer type</A>. Each value of a
discrete type has a position
number that is an integer value. Indexing and iteration
rules use values of discrete types. (&#167;3.1)<P>

<B>B.78 <A NAME="driver"> driver</A>:</B> A container for a <A
HREF="#projected output waveform">projected output waveform</A> of a
<A HREF="#signal">signal</A>. The value of the <A
HREF="#signal">signal</A> is a function of the
<A HREF="#current value"> current values</A> of its <A HREF="#driver">
drivers</A>. Each
process that assigns to a given <A HREF="#signal">signal</A>
implicitly contains a <A HREF="#driver">driver</A> for that <A
HREF="#signal">signal</A>. A <A HREF="#signal">signal</A> assignment
statement affects only the <A HREF="#associated driver">associated
driver(s)</A>. (&#167;12.4.4, &#167;12.6.1, &#167;12.6.2,
&#167;12.6.3)<P>

<B>B.79 <A NAME="driving value"> driving value</A>:</B> The value a <A
HREF="#signal">signal</A> provides as a <A HREF="#source">source</A>
of other <A HREF="#signal">signals</A>. (&#167;12.6.2)<P>

<B>B.80 <A NAME="effective value"> effective value</A>:</B> The value
obtained by evaluating a reference to the <A
HREF="#signal">signal</A> within an <A
HREF="#expression">expression</A>. (&#167;12.6.2)<P>

<B>B.81 <A NAME="elaboration"> elaboration</A>:</B> The process by
which a <A HREF="#declaration">declaration</A> achieves its
effect. Prior to the completion of its  elaboration (including before the
elaboration), a <A HREF="#declaration">declaration</A> is not yet
elaborated. (&#167;12)<P>

<B>B.82 <A NAME="element">element</A>:</B> A constituent of a <A
HREF="#composite type">composite type</A>. (&#167;3) <I>See also</I> <A
HREF="#subelement"> subelement</A>.<P>

<B>B.83 <A NAME="entity declaration"> entity declaration</A>:</B> A
definition of the interface between a given <A HREF="#design entity">
design entity</A> and the environment in which it is used. It
may also specify <A HREF="#declaration">declarations</A> and
statements that are part of the <A HREF="#design entity">design
entity</A>. A given <A HREF="#entity declaration">entity
declaration</A> may be shared by many design entities, each of which
has a different architecture. Thus, an <A HREF="#entity declaration">
entity declaration</A> can potentially represent a class
of design entities, each with the same interface. (&#167;1,
&#167;1.1)<P>

<B>B.84 <A NAME="enumeration literal"> enumeration literal</A>:</B> A
<A HREF="#literal">literal</A> of an <A HREF="#enumeration type">
enumeration type</A>. An enumeration literal may be either
an identifier or a <A
HREF="#character literal">character literal</A>. (&#167;5.1.1,
&#167;7.3.1)<P>

<B>B.85 <A NAME="enumeration type"> enumeration type</A>:</B> A <A
HREF="#type">type</A> whose values are defined by listing
(enumerating) them. The values of the <A HREF="#type">type</A> are
represented by <A HREF="#enumeration literal">enumeration
literals</A>. (&#167;3.1, &#167;3.1.1)<P>

<A HREF="#Example13">[Example E.13]</A>

<p>

<B>B.86 <A NAME="error"> error</A>:</B> A condition that makes the
source description illegal. If an  error is detected at the time of <A
HREF="#analysis">analysis</A> of a <A HREF="#design unit">design
unit</A>, it prevents the creation of a <A HREF="#library unit">
library unit</A> for the given <A HREF="#design unit">design
unit</A>. A run-time error causes simulation to
terminate. (&#167;11.4)<P>

<B>B.87 <A NAME="erroneous"> erroneous</A>:</B> An <A
HREF="#error">error</A> condition that cannot always be
detected. (&#167;2.1.1.1, &#167;2.2)<P>

<B>B.88 <A NAME="event"> event</A>:</B> A change in the <A
HREF="#current value">current value</A> of a <A
HREF="#signal">signal</A>, which occurs when the <A
HREF="#signal">signal</A> is updated with its
<A HREF="#effective value">effective value</A>. (&#167;12.6.2)<P>

<B>B.89 <A NAME="execute"> execute</A>:</B><P>

<ol> <li>When first the <A HREF="#design hierarchy">design
hierarchy</A> of a <A HREF="#model">model</A> is elaborated, then its
<A HREF="#net">nets</A> are initialized, and finally simulation
proceeds with repetitive execution of the <A HREF="#simulation cycle">
simulation cycle</A>, during which processes are executed and
<A HREF="#net">nets</A> are updated.</li> <li>When a process performs
the actions specified by the algorithm described in its statement
part. (&#167;12, 12.6)</li> </ol><P>

<B>B.90 <A NAME="expanded name"> expanded name</A>:</B> A <A
HREF="#selected name">selected name</A> (in the syntactic sense) that
denotes one or all of the <A
HREF="#primary">primary</A> units in a <A HREF="#library">library</A>
or any <A HREF="#named entity">named entity</A> within a <A
HREF="#primary">primary</A> unit. (&#167;6.3, &#167;8.1) <I>See also</I> <A
HREF="#selected name">selected name</A>.<P>

<B>B.91 <A NAME="explicit ancestor"> explicit ancestor</A>:</B> The
parent of the <A HREF="#implicit signal">implicit
signal</A> that is defined by the predefined <A
HREF="#attribute">attributes</A> &#39;DELAYED, &#39;QUIET, &#39;STABLE, or
&#39;TRANSACTION. It is determined using the prefix of the <A
HREF="#attribute">attribute</A>. If the prefix denotes
an <A HREF="#explicit signal">explicit
signal</A> or (or <A HREF="#member">member</A> thereof), then that is
the explicit ancestor of the <A
HREF="#implicit signal">implicit signal</A>. If the prefix is one of
the <A HREF="#implicit signal">implicit signals</A> defined by the
predefined <A HREF="#attribute">attributes</A> &#39;DELAYED, &#39;QUIET,
&#39;STABLE, or &#39;TRANSACTION, this rule is applied recursively. If the
prefix is an <A HREF="#guard">implicit signal GUARD</A>,
the <A HREF="#signal">signal</A> has no explicit ancestor</A>.
(&#167;2.2)<P>

<B>B.92 <A NAME="explicit signal"> explicit signal</A>:</B> A <A
HREF="#signal">signal</A> defined by the predefined <A
HREF="#attribute">attributes</A> &#39;DELAYED, &#39;QUIET, &#39;STABLE, or
&#39;TRANSACTION. (&#167;2.2)<P>

<B>B.93 <A NAME="explicitly declared constant"> explicitly declared
constant</A>:</B> A <A HREF="#constant">constant</A> of a specified <A
HREF="#type">type</A> that is declared by a <A
HREF="#constant">constant</A> <A
HREF="#declaration">declaration</A>. (&#167;4.3.1.1)<P>

<B>B.94 <A NAME="explicitly declared object"> explicitly declared
object</A>:</B> An <A HREF="#object">object</A> of a specified <A
HREF="#type">type</A> that is declared by an <A
HREF="#object">object</A> <A HREF="#declaration">declaration</A>. An
<A HREF="#object">object</A> <A HREF="#declaration">declaration</A> is
called a <A HREF="#single-object declaration">single-object
declaration</A> if its identifier list has a single identifier; it is
called a <I>multiple-object declaration</I> if the identifier list has two or
more identifiers. (&#167;4.3, &#167;4.3.1) <I>See also</I>
<A HREF="#implicitly declared object">implicitly declared object</A>.<P>

<B>B.95 <A NAME="expression"> expression</A>:</B> A formula that
defines the computation of a value. (&#167;7.1)<P>

<B>B.96 <A NAME="extend"> extend</A>:</B> A property of
source text forming a <A HREF="#declarative region">
declarative region</A> with disjoint parts. In a <A
HREF="#declarative region">declarative region</A> with disjoint parts,
if a portion of text is said to <I>extend</I> from some
specific point of a <A HREF="#declarative region">declarative
region</A> to the end of the region, then this portion is the
corresponding subset of the <A HREF="#declarative region">declarative
region</A> (and does not include intermediate declarative items
between an interface <A HREF="#declaration">declaration</A> and a
corresponding body <A
HREF="#declaration">declaration</A>). (&#167;10.1)<P>

<B>B.97 <A NAME="extended digit"> extended digit</A>:</B> A lexical
element that is either a digit or a letter. (&#167;13.4.2)<P>

<B>B.98 <A NAME="external block"> external block</A>:</B> A top-level
<A HREF="#design entity">design entity</A> that resides in a <A
HREF="#library">library</A> and may be used as a component in other
designs. (&#167;1)<P>

<B>B.99 <A NAME="file type"> file type</A>:</B> A <A
HREF="#type">type</A> that provides access to <A
HREF="#object">objects</A> containing a sequence of values of a given
<A HREF="#type">type</A>. <A HREF="#file type">File types</A> are
typically used to access files in the host system environment. The
value of a file <A HREF="#object">object</A> is the sequence of values
contained in the host system file. (&#167;3, &#167;3.4)<P>

<B>B.100 <A NAME="floating point types"> floating point types</A>:</B>
A discrete <A HREF="#scalar type">scalar type</A> whose values
approximate real numbers. The representation of a floating point <A
HREF="#type">type</A> includes a minimum of six decimal digits of
precision. (&#167;3.1, &#167;3.1.4)<P>

<B>B.101 <A NAME="foreign subprogram"> foreign subprogram</A>:</B> A
subprogram that is decorated with the <A
HREF="#attribute">attribute</A> &#39;FOREIGN, defined in package
STANDARD. The STRING value of the <A HREF="#attribute">attribute</A>
may specify implementation-dependent information about the <A
HREF="#foreign subprogram">foreign subprogram</A>. Foreign subprograms
may have non-VHDL implementations. An implementation may place
restrictions on the allowable <A HREF="#mode">modes</A>, classes, and
<A HREF="#type">types</A> of the <A HREF="#formal">formal
parameters</A> to a foreign subprogram, such as constraints
on the number and allowable order
of the <A HREF="#parameter">parameters</A>. (&#167;2.2)<P>

<B>B.102 <A NAME="formal"> formal</A>:</B> A formal <A
HREF="#port">port</A> or formal <A
HREF="#generic">generic</A> of a <A
HREF="#design entity">design entity</A>, a <A HREF="#block">block</A>
statement, or a formal <A HREF="#parameter">parameter</A>
of a subprogram. (&#167;2.1.1,
&#167;4.3.2.2, &#167;5.2.1.2, &#167;9.1)<P>

<B>B.103 <A NAME="full declaration"> full declaration</A>:</B> A <A
HREF="#constant">constant</A> <A HREF="#declaration">declaration</A>
occurring in a package body with the same identifier as that of a <A
HREF="#deferred constant">deferred constant</A> <A
HREF="#declaration">declaration</A> in the corresponding package <A
HREF="#declaration">declaration</A>. A full <A HREF="#type">type</A>
<A HREF="#declaration">declaration</A> is a <A HREF="#type">type</A>
<A HREF="#declaration">declaration</A> corresponding to an <A
HREF="#incomplete type declaration">incomplete type
declaration</A>. (&#167;2.6)<P>

<A HREF="#Example11">[Example E.11]</A>

<p>

<B>B.104 <A NAME="fully bound"> fully bound</A>:</B> A <A
HREF="#binding">binding</A> indication for the component <A
HREF="#instance">instance</A> implies an entity interface and an
architecture. (&#167;5.2.1.1)<P>

<B>B.105 <A NAME="generate parameter"> generate parameter</A>:</B> A
<A HREF="#constant">constant</A> <A HREF="#object">object</A> whose <A
HREF="#type">type</A> is the <A HREF="#base type">base type</A> of the <A
HREF="#discrete range">discrete range</A> of a
<A HREF="#generate parameter">generate parameter</A> <A
HREF="#specification">specification</A>. A
<A HREF="#generate parameter">generate parameter</A> is declared by
a generate statement. (&#167;9.7)<P>

<B>B.106 <A NAME="generic"> generic</A>:</B> An interface <A
HREF="#constant">constant</A> declared in the <A
HREF="#block">block</A> header of a <A HREF="#block">block</A>
statement, a component <A HREF="#declaration">declaration</A>, or an
<A HREF="#entity declaration">entity declaration</A>.
Generics provide a channel for <A
HREF="#static">static</A> information to be communicated to a <A
HREF="#block">block</A> from its environment. Unlike <A
HREF="#constant">constants</A>, however, the value of a <A
HREF="#generic">generic</A> can be supplied externally, either in a
component instantiation statement or in a <A
HREF="#configuration">configuration specification</A>.
(&#167;1.1.1.1)<P>

<B>B.107 <A NAME="generic interface list"> generic interface
list</A>:</B> A list that defines local or <A
HREF="#formal">formal</A> <A HREF="#generic">generic</A> <A
HREF="#constant">constants</A>. (&#167;1.1.1.1, &#167;4.3.2.1)<P>

<B>B.108 <A NAME="globally static expression"> globally static
expression</A>:</B> An <A HREF="#expression">expression</A> that can
be evaluated as soon as the <A HREF="#design hierarchy">design
hierarchy</A> in which it appears is elaborated. A <A
HREF="#locally static expression">locally static expression</A> is also
globally static unless the <A
HREF="#expression">expression</A> appears in a dynamically elaborated
context. (&#167;7.4)<P>

<B>B.109 <A NAME="globally static primary"> globally static
primary</A>:</B> A <A HREF="#primary">primary</A> whose value can be
determined during the <A HREF="#elaboration">elaboration</A> of its <A
HREF="#complete context">complete context</A> and that does not
thereafter change. Globally <A HREF="#static">static</A> primaries can
only appear within statically elaborated contexts. (&#167;7.4.2)<P>

<B>B.110 <A NAME="group"> group</A>:</B> A named collection of <A
HREF="#named entity">name entities</A>. Groups
relate different <A HREF="#named entity">name entities</A> for the
purposes not specified by the language. In particular,
groups may be decorated with <A
HREF="#attribute">attributes</A>. (&#167;4.6, &#167;4.7)<P>

<B>B.111 <A NAME="guard"> guard</A>:</B> <I>See</I>
<A HREF="#guard expression">guard expression</A>.<P>

<B>B.112 <A NAME="guard expression"> guard expression</A>:</B> A
Boolean-valued <A HREF="#expression">expression</A> associated with a
<A HREF="#block">block</A> statement that controls assignments to <A
HREF="#guarded signal">guarded signals</A> within the <A
HREF="#block">block</A>. A guard
expression defines an <A HREF="#implicit signal">implicit
signal</A> <A HREF="#guard">GUARD</A> that may be used to control the
operation of certain statements within the <A
HREF="#block">block</A>. (&#167;4.3.1.2, &#167;9.1, &#167;9.5)<P>

<B>B.113 <A NAME="guarded assignment"> guarded assignment</A>:</B> A
concurrent <A HREF="#signal">signal</A> assignment statement that
includes the option <B>guarded</B>, which specifies that the <A
HREF="#signal">signal</A> assignment statement is executed when a <A
HREF="#signal">signal</A> <A HREF="#guard">GUARD</A> changes from
FALSE to TRUE, or when that <A HREF="#signal">signal</A> has been TRUE
and an <A HREF="#event">event</A> occurs on one of the <A
HREF="#signal">signals</A> referenced in the corresponding <A
HREF="#guard expression">GUARD expression</A>. The <A
HREF="#signal">signal</A> <A HREF="#guard">GUARD</A> may be one of the
implicitly declared <A HREF="#guard">GUARD</A> <A
HREF="#signal">signals</A> associated with <A HREF="#block">block</A>
statements that have <A HREF="#guard expression">guard
expressions</A>, or it may be an explicitly declared <A
HREF="#signal">signal</A> of <A HREF="#type">type</A> Boolean that is
<A HREF="#visible">visible</A> at the point of the concurrent <A
HREF="#signal">signal</A> assignment statement. (&#167;9.5)<P>

<B>B.114 <A NAME="guarded signal"> guarded signal</A>:</B> A <A
HREF="#signal">signal</A> declared as a <A
HREF="#register">register</A> or a <A HREF="#bus">bus</A>. Such <A
HREF="#signal">signals</A> have special semantics when their <A
HREF="#driver">drivers</A> are updated from within
<A HREF="#guarded signal">guarded signal</A> assignment statements.
(&#167;4.3.1.2)<P>

<B>B.115 <A NAME="guarded target"> guarded target</A>:</B> A <A
HREF="#signal">signal</A> assignment target consisting only of <A
HREF="#guarded signal">guarded signals</A>. An unguarded target is a
target consisting only of unguarded <A
HREF="#signal">signals</A>. (&#167;9.5)<P>

<B>B.116 <A NAME="hidden"> hidden</A>:</B> A <A
HREF="#declaration">declaration</A> that is not
<A HREF="#directly visible">directly visible</A>. A <A
HREF="#declaration">declaration</A> may be
<I>hidden</I> in its <A HREF="#scope">scope</A> by a <A
HREF="#homograph">homograph</A> of the <A
HREF="#declaration">declaration</A>. (&#167;10.3)<P>

<B>B.117 <A NAME="homograph"> homograph</A>:</B> A reflexive property
of two <A HREF="#declaration">declarations</A>. Each of two <A
HREF="#declaration">declarations</A> is said to be a
<I>homograph</I> of the other if both <A
HREF="#declaration">declarations</A> have the same identifier and
overloading is allowed for at most one of the two. If
<A HREF="#overloaded">overloading</A> is
allowed for both <A HREF="#declaration">declarations</A>, then each of
the two is a <A HREF="#homograph">homograph</A> of the other if they
have the same identifier, operator symbol, or
<A HREF="#character literal">character literal</A>, as well as the
same <A HREF="#parameter and result type profile">parameter and
result type profile</A>. (&#167;1.3.1, &#167;10.3)<P>

<B>B.118 <A NAME="identify"> identify</A>:</B> A property of a <A
HREF="#name">name</A> appearing in an element association of an
assignment target in the form of an <A
HREF="#aggregate">aggregate</A>. The <A HREF="#name">name</A> is said
to <I>identify</I> a <A HREF="#signal">signal</A> or
<A HREF="#variable">variable</A> and any <A
HREF="#subelement">subelements</A> of that <A
HREF="#signal">signal</A> or <A
HREF="#variable">variable</A>. (&#167;8.4, &#167;8.5)<P>

<B>B.119 <A NAME="immediate scope"> immediate scope</A>:</B> A
property of a <A HREF="#declaration">declaration</A> with respect to
the <A HREF="#declarative region">declarative region</A> within which
the <A HREF="#declaration">declaration</A> immediately occurs. The
immediate scope of the <A
HREF="#declaration">declaration</A> extends from
the beginning of the <A HREF="#declaration">declaration</A> to the end
of the <A HREF="#declarative region">declarative
region</A>. (&#167;10.2)<P>

<B>B.120 <A NAME="immediately within"> immediately within</A>:</B> A
property of a <A HREF="#declaration">declaration</A> with respect to
some <A HREF="#declarative region">declarative region</A>. A <A
HREF="#declaration">declaration</A> is said to occur <I>immediately
within</I> a <A HREF="#declarative region">declarative region</A> if this
region is the innermost region that encloses the <A
HREF="#declaration">declaration</A>, not counting the <A
HREF="#declarative region">declarative region</A> (if any) associated
with the <A HREF="#declaration">declaration</A>
itself. (&#167;10.1)<P>

<B>B.121 <A NAME="implicit signal"> implicit signal</A>:</B> Any <A
HREF="#signal">signal</A> S&#39;Stable(T), S&#39;Quiet(T), S&#39;Delayed, or
S&#39;Transaction, or any implicit <A HREF="#guard">GUARD signal</A>.
A <A HREF="#member">member</A> of an implicit signal is also an
implicit signal. (&#167;12.6.2,&#167;12.6.3, &#167;12.6.4)<P>

<B>B.122 <A NAME="implicitly declared object">implicitly declared
object</A>:</B> An <A HREF="#object">object</A> whose <A
HREF="#declaration">declaration</A> is not explicit in the
source description, but is a consequence of other
constructs; for example, <A HREF="#guard">signal GUARD</A>.
(&#167;4.3, &#167;9.1, &#167;14.1) <I>See also</I>
<A HREF="#explicitly declared object"> explicitly declared
object</A>.<P>

<B>B.123 <A NAME="imply"> imply</A>:</B> A property of a <A
HREF="#binding">binding</A> indication in a <A
HREF="#configuration">configuration</A> <A
HREF="#specification">specification</A> with respect to the <A
HREF="#design entity">design entity</A> indicated by the <A
HREF="#binding">binding</A> <A
HREF="#specification">specification</A>. The <A
HREF="#binding">binding</A> indication is said to
<I>imply</I> the <A HREF="#design entity">design
entity</A>; the <A HREF="#design entity">design entity</A> may be
indicated directly, indirectly, or by default. (&#167;5.2.1.1)<P>

<B>B.124 <A NAME="impure function"> impure function</A>:</B> A
function that may return a different value each time it is called,
even when different calls have the same actual
<A HREF="#parameter">parameter</A> values. A <A HREF="#pure function">
pure function</A> returns the same value each time it is
called using the same values as <A HREF="#actual">actual</A> <A
HREF="#parameter">parameters</A>. A impure
function can <A HREF="#update">update</A> <A
HREF="#object">objects</A> outside of its <A HREF="#scope">scope</A>
and can access a broader class of values than a
<A HREF="#pure function">pure function</A>. (&#167;2)<P>

<B>B.125 <A NAME="incomplete type declaration"> incomplete type
declaration</A>:</B> A <A HREF="#type">type</A> <A
HREF="#declaration">declaration</A> that is used to {define} mutually
dependent and recursive <A HREF="#access type">access
types</A>. (&#167;3.3.1)<P>

<A HREF="#Example12">[Example E.12]</A>

<p>

<B>B.126 <A NAME="index constraint"> index constraint</A>:</B> A <A
HREF="#constraint">constraint</A> that determines the
<A HREF="#index range">index range</A> for every index of an <A
HREF="#array type">array type</A>, and thereby the
bounds of  the array. An index constraint is
<I>compatible</I> with an <A HREF="#array type">array type</A> if and only if
the <A HREF="#constraint">constraint</A> defined by each <A
HREF="#discrete range">discrete range</A> in the
index constraint is compatible with the corresponding
<A HREF="#index subtype">index subtype</A> in the
<A HREF="#array type">array type</A>. An array value <I>satisfies</I> an
index constraint if the array value and the
index constraint have the same <A
HREF="#index range">index range</A> at each index position
. (&#167;3.1, &#167;3.2.1.1)<P>

<B>B.127 <A NAME="index range"> index range</A>:</B> A
multidimensional array has a distinct element for each possible
sequence of index values that can be formed by selecting one value for
each index (in the given order). The possible values for a given index
are all the values that belong to the corresponding <A
HREF="#range">range</A>. This <A HREF="#range">range</A> of values is
called the <I>index range</I>. (&#167;3.2.1)<P>

<B>B.128 <A NAME="index subtype"> index subtype</A>:</B> For a given
index position of an array, the <I>index subtype</I>
is denoted by the <A HREF="#type">type</A> mark of the
corresponding index <A HREF="#subtype">subtype</A>
definition. (&#167;3.2.1)<P>

<B>B.129 <A NAME="inertial delay">inertial delay</A>:</B> A delay <A
HREF="#model">model</A> used for switching circuits; a pulse whose
duration is shorter than the switching time of the circuit will not be
transmitted. Inertial delay is the default delay
mode for <A HREF="#signal">signal</A> assignment
statements. (&#167;8.4) <I>See also</I> <A HREF="#transport delay"> transport
delay</A>.<P>

<A HREF="#Example15">[Example E.15]</A>

<p>

<B>B.130 <A NAME="initial value expression"> initial value
expression</A>:</B> An <A HREF="#expression">expression</A> that
specifies the initial value to be assigned to a <A
HREF="#variable">variable</A>. (&#167;4.3.1.3)<P>

<B>B.131 <A NAME="inputs"> inputs</A>:</B> The <A
HREF="#signal">signals</A> identified by the
<A HREF="#longest static prefix">longest static prefix</A> of each
<A HREF="#signal">signal</A>
<A HREF="#name">name</A> appearing as a <A HREF="#primary">primary</A>
in each <A HREF="#expression">expression</A> (other than time <A
HREF="#expression">expressions</A>) within a concurrent <A
HREF="#signal">signal</A> assignment statement. (&#167;9.5)<P>

<B>B.132 <A NAME="instance"> instance</A>:</B> A subcomponent of a <A
HREF="#design entity">design entity</A> whose prototype is a component
<A HREF="#declaration">declaration</A>, <A HREF="#design entity">
design entity</A>, or <A
HREF="#configuration">configuration</A> <A
HREF="#declaration">declaration</A>. Each
instance of a component may have different <A
HREF="#actual">actuals</A> associated with its
<A HREF="#local port">local ports</A> and <A
HREF="#generic">generics</A>. A component instantiation statement
whose instantiated unit denotes a component
creates an instance of the corresponding component. A
component instantiation statement whose instantiated unit
denotes either a <A HREF="#design entity">design
entity</A> or a <A HREF="#configuration">configuration</A> <A
HREF="#declaration">declaration</A> creates an
instance of the denoted <A HREF="#design entity">
design entity</A>. (&#167;9.6, &#167;9.6.1, &#167;9.6.2)<P>

<B>B.133 <A NAME="integer literal"> integer literal</A>:</B> An <A
HREF="#abstract literal">abstract literal</A> of the <A
HREF="#type">type</A> <A
HREF="#universal_integer">universal_integer</A> that does not contain
a base point. (&#167;13.4)<P>

<B>B.134 <A NAME="integer type"> integer type</A>:</B> A discrete <A
HREF="#scalar type">scalar type</A> whose values represent integer
numbers within a specified <A HREF="#range">range</A>. (&#167;3.1,
&#167;3.1.2)<P>

<A HREF="#Example14">[Example E.14]</A>

<p>

<B>B.135 <A NAME="interface list"> interface list</A>:</B> A list that
declares the interface <A HREF="#object">objects</A> required by a
subprogram, component, <A HREF="#design entity">design entity</A>, or
<A HREF="#block">block</A> statement. (&#167;4.3.2.1)<P>

<B>B.136 <A NAME="internal block"> internal block</A>:</B> A nested <A
HREF="#block">block</A> in a <A HREF="#design unit">design unit</A>,
as defined by a <A HREF="#block">block</A> statement. (&#167;1)<P>

<A HREF="#Example8">[Example E.8]</A>

<p>

<B>B.137 <A NAME="ISO"> ISO</A>:</B> The International Organization
for Standardization.<P>

<B>B.138 <A NAME="ISO 8859-1"> ISO 8859-1</A>:</B> The <A
HREF="#ISO">ISO</A> Latin-l character set. Package Standard contains
the definition of <A HREF="#type">type</A> Character, which represents
the <A HREF="#ISO">ISO</A> Latin-l character set. (&#167;3.1.1,
&#167;14.2)<P>

<B>B.139 <A NAME="kernel process"> kernel process</A>:</B> A
conceptual representation of the agent that coordinates the activity
of user-defined processes during a simulation. The
kernel process causes the execution of I/O operations,
the propagation of <A HREF="#signal">signal</A> values, and the
updating of values of <A HREF="#implicit signal">implicit signals</A>
[such as S&#39;Stable(T)]; in addition, it detects <A
HREF="#event">events</A> that occur and causes the
appropriate processes to <A
HREF="#execute">execute</A> in response to those <A
HREF="#event">events</A>. (&#167;12.6)<P>

<B>B.140 <A NAME="left of"> left of</A>:</B> When both a value V1 and
a value V2 <A HREF="#belong (to a range)">belong to a range</A> and
either the <A HREF="#range">range</A> is an
<A HREF="#ascending range">ascending range</A> and V2 is the successor
of V1, or the <A HREF="#range">range</A> is a
<A HREF="#descending range">descending
range</A> and V2 is the predecessor of V1. (&#167;3.1)<P>

<B>B.141 <A NAME="left-to-right order"> left-to-right order</A>:</B>
When each value in a list of values is to
the left of the next value in the list within that <A
HREF="#range">range</A>, except for the last value in the
list. (&#167;3.1)<P>

<B>B.142 <A NAME="library"> library</A>:</B> <I>See</I>
<A HREF="#design library">design library</A>.<P>

<B>B.143 <A NAME="library unit"> library unit</A>:</B> The
representation in a <A HREF="#design library">design library</A> of an
analyzed <A HREF="#design unit">design unit</A>. (&#167;11.1)<P>

<B>B.144 <A NAME="literal"> literal</A>:</B> A value that is directly
specified in the description of a design. A <A
HREF="#literal">literal</A> can be a <A HREF="#bit string literal">bit
string literal</A>, <A HREF="#enumeration literal">enumeration
literal</A>, <A HREF="#numeric literal">numeric literal</A>, <A
HREF="#string literal">string literal</A>, or the <A
HREF="#literal">literal</A> <B>null</B>. (&#167;7.3.1)<P>

<B>B.145 <A NAME="local generic"> local generic</A>:</B> An interface
<A HREF="#object">object</A> declared in a component <A
HREF="#declaration">declaration</A> that serves to connect a <A
HREF="#formal">formal generic</A> in the <A
HREF="#interface list">interface list</A> of an entity and an <A
HREF="#actual">actual generic</A> or value in
the <A HREF="#design unit">design unit</A> instantiating that
entity. (&#167;4.3, &#167;4.3.2.2, &#167;4.5)<P>

<B>B.146 <A NAME="local port"> local port</A>:</B> A <A
HREF="#signal">signal</A> declared in the
<A HREF="#interface list">interface list</A> of a component <A
HREF="#declaration">declaration</A> that serves to connect a <A
HREF="#formal">formal port</A> in the <A
HREF="#interface list">interface list</A> of an entity and an <A
HREF="#actual">actual port</A> or <A
HREF="#signal">signal</A> in the <A HREF="#design unit">design
unit</A> instantiating that entity. (&#167;4.3, &#167;4.3.2.2,
&#167;4.5)<P>

<B>B.147 <A NAME="locally static expression"> locally static
expression</A>:</B> An <A HREF="#expression">expression</A> that can
be evaluated during the <A HREF="#analysis">analysis</A> of the <A
HREF="#design unit">design unit</A> in which it appears. (&#167;7.4,
&#167;7.4.1)<P>

<B>B.148 <A NAME="locally static name"> locally static name</A>:</B> A
<A HREF="#name">name</A> in which every <A
HREF="#expression">expression</A> is locally <A
HREF="#static">static</A> (if every <A HREF="#discrete range">discrete
range</A> that appears as part of the <A HREF="#name">name</A>
denotes a locally <A HREF="#static range">static
range</A> or <A HREF="#subtype">subtype</A> and if no prefix within
the <A HREF="#name">name</A> is either an <A HREF="#object">object</A>
or value of an <A HREF="#access type">access type</A> or a function
call). (&#167;6.1)<P>

<B>B.149 <A NAME="locally static primary"> locally static
primary</A>:</B> One of a certain group of
primaries that includes <A HREF="#literal">literals</A>, certain <A
HREF="#constant">constants</A>, and certain <A
HREF="#attribute">attributes</A>. (&#167;7.4)<P>

<B>B.150 <A NAME="locally static subtype"> locally static
subtype</A>:</B> A <A HREF="#subtype">subtype</A> whose <A
HREF="#bound">bounds</A> and direction can be determined during the <A
HREF="#analysis">analysis</A> of the <A HREF="#design unit">design
unit</A> in which it appears. (&#167;7.4.1)<P>

<B>B.151 <A NAME="longest static prefix"> longest static
prefix</A>:</B> The <A HREF="#name">name</A> of a <A
HREF="#signal">signal</A> or a <A HREF="#variable">variable</A> <A
HREF="#name">name</A>, if the <A HREF="#name">name</A> is a <A
HREF="#static signal name">static signal</A> or <A
HREF="#static variable name">variable name</A>. Otherwise, the
<A HREF="#longest static prefix">longest static prefix</A> is the
longest prefix of the <A HREF="#name">name</A> that is a <A
HREF="#static signal name">static signal</A> or <A
HREF="#static variable name">variable name</A>. (&#167;6.1)
<I>See also</I> <A HREF="#static signal name">static signal name</A>.<P>

<B>B.152 <A NAME="loop parameter"> loop parameter</A>:</B> A <A
HREF="#constant">constant</A>, implicitly declared by the for clause
of a loop statement, used to count the number of iterations of a
loop. (&#167;8.9)<P>

<B>B.153 <A NAME="lower bound"> lower bound</A>:</B> For a nonnull <A
HREF="#range">range</A> L <B>to</B> R or L <B>downto</B> R, the smaller of L and
R. (&#167;3.1)<P>

<B>B.154 <A NAME="match"> match</A>:</B> A property of a signature
with respect to the <A HREF="#parameter">parameter</A> and <A
HREF="#subtype">subtype</A> profile of a subprogram or <A
HREF="#enumeration literal">enumeration literal</A>. The signature is
said to <I>match</I> the <A HREF="#parameter and result type profile">
parameter and result type profile</A> if certain
conditions are true. (&#167;2.3.2)<P>

<B>B.155 <A NAME="matching elements"> matching elements</A>:</B>
Corresponding elements of two <A HREF="#composite type">composite
type</A> values that are used for certain logical and relational
operations. (&#167;7.2.3)<P>

<B>B.156 <A NAME="member"> member</A>:</B> A <A
HREF="#slice">slice</A> of an <A HREF="#object">object</A>, a <A
HREF="#subelement">subelement</A>, or an <A HREF="#object">object</A>;
or a <A HREF="#slice">slice</A> of a <A
HREF="#subelement">subelement</A> of an <A
HREF="#object">object</A>. (&#167;3)<P>

<B>B.157 <A NAME="mode"> mode</A>:</B> The direction of information
flow through the <A HREF="#port">port</A> or <A
HREF="#parameter">parameter</A>. Modes are <B>in</B>,
<B>out</B>, <B>inout</B>, <B>buffer</B>, or <B>linkage</B>. (&#167;4.3.2)<P>

<B>B.158 <A NAME="model"> model</A>:</B> The result of the <A
HREF="#elaboration">elaboration</A> of a
<A HREF="#design hierarchy">design hierarchy</A>. The <I>model</I> can be
executed in order to simulate the design it represents. (&#167;12,
&#167;12.6)<P>

<B>B.159 <A NAME="name"> name</A>:</B> A property of an identifier
with respect to some <A HREF="#named entity">named entity</A>. Each
form of <A HREF="#declaration">declaration</A> associates an
identifier with a <A HREF="#named entity">named entity</A>. In certain
places within the <A HREF="#scope">scope</A> of a <A
HREF="#declaration">declaration</A>, it is valid to use the identifier
to refer to the associated <A HREF="#named entity">named entity</A>;
these places are defined by the visibility rules. At such places, the
identifier is said to be the <I>name</I> of the <A
HREF="#named entity">named entity</A>. (&#167;4, &#167;6.1)<P>

<B>B.160 <A NAME="named association"> named association</A>:</B> An <A
HREF="#association element">association element</A> in which the <A
HREF="#formal">formal</A> <A HREF="#designator">designator</A> appears
explicitly. (&#167;4.3.2.2, &#167;7.3.2)<P>

<B>B.161 <A NAME="named entity"> named entity</A>:</B> An item
associated with an identifier, <A HREF="#character literal">character
literal</A>, or operator symbol as the result of an explicit or
implicit <A HREF="#declaration">declaration</A>. (&#167;4) <I>See also</I> <A
HREF="#name">name</A>.<P>

<B>B.162 <A NAME="net"> net</A>:</B> A collection of <A
HREF="#driver">drivers</A>, <A HREF="#signal">signals</A> (including
<A HREF="#port">ports</A> and <A HREF="#implicit signal">implicit
signals</A>), <A HREF="#conversion function">conversion functions</A>,
and <A HREF="#resolution function">resolution functions</A> that
connect different processes. Initialization of a net occurs after <A
HREF="#elaboration">elaboration</A>, and a net is
updated during each <A HREF="#simulation cycle">simulation
cycle</A>. (&#167;12, &#167;12.1, &#167;12.6.2)<P>

<B>B.163 <A NAME="nonobject alias"> nonobject alias</A>:</B> An <A
HREF="#alias">alias</A> whose <A HREF="#designator">designator</A>
denotes some <A HREF="#named entity">named
entity</A> other than an <A HREF="#object">object</A>. (&#167;4.3.3,
&#167;4.3.3.2) <I>See also</I> <A HREF="#object alias">object alias</A>.<P>

<B>B.164 <A NAME="nonpostponed process"> nonpostponed process</A>:</B>
An explicit or implicit process whose source
statement does not contain the reserved word <B>postponed</B>. When a
nonpostponed process is resumed, it
<A HREF="#execute">executes</A> in the current
<A HREF="#simulation cycle">simulation cycle</A>. Thus, nonpostponed
processes have access to the <A HREF="#current value">current values</A>
of <A HREF="#signal">signals</A>, whether or not those values are
stable at the current <A HREF="#model">model</A> time. (&#167;9.2)<P>

<B>B.165 <A NAME="null array"> null array</A>:</B> Any of the <A
HREF="#discrete range">discrete ranges</A> in the
<A HREF="#index constraint">index constraint</A> of an array that
define a <A HREF="#null range">null range</A>. (&#167;3.2.1.1)<P>

<B>B.166 <A NAME="null range"> null range</A>:</B> A <A
HREF="#range">range</A> that specifies an empty subset of values. A <A
HREF="#range">range</A> L <B>to</B> R is a <A HREF="#null range">null
range</A> if L &gt; R, and <A HREF="#range">range</A> L <B>downto</B> R is a
<A HREF="#null range">null range</A> if L &lt; R. (&#167;3.1)<P>

<B>B.167 <A NAME="null slice"> null slice</A>:</B> A <A
HREF="#slice">slice</A> whose <A HREF="#discrete range">discrete
range</A> is a <A HREF="#null range">null range</A>. (&#167;6.5)<P>

<B>B.168 <A NAME="null waveform element"> null waveform
element</A>:</B> A <A HREF="#waveform">waveform</A> element that is
used to turn off a <A HREF="#driver">driver</A> of a
<A HREF="#guarded signal">guarded signal</A>. (&#167;8.4.1)<P>

<B>B.169 <A NAME="null transaction"> null transaction</A>:</B> A <A
HREF="#transaction">transaction</A> produced by evaluating a <A
HREF="#null waveform element">null waveform
element</A>. (&#167;8.4.1)<P>

<B>B.170 <A NAME="numeric literal"> numeric literal</A>:</B> An <A
HREF="#abstract literal">abstract literal</A>, or a <A
HREF="#literal">literal</A> of a <A HREF="#physical type">physical
type</A>. (&#167;7.3.1)<P>

<B>B.171 <A NAME="numeric type"> numeric type</A>:</B> An <A
HREF="#integer type">integer type</A>, a <A HREF="#floating point types">
floating point type</A>, or a <A HREF="#physical type">physical
type</A>. (&#167;3.1)<P>

<B>B.172 <A NAME="object"> object</A>:</B> A
<A HREF="#named entity">named entity</A> that has a value of a given <A
HREF="#type">type</A>. An <A HREF="#object">object</A> can be a <A
HREF="#constant">constant</A>, <A HREF="#signal">signal</A>, <A
HREF="#variable">variable</A>, or file. (&#167;4.3.3)<P>

<B>B.173 <A NAME="object alias"> object alias</A>:</B> An <A
HREF="#alias">alias</A> whose <A HREF="#alias">alias</A> <A
HREF="#designator">designator</A> denotes an <A
HREF="#object">object</A> (that is, a <A
HREF="#constant">constant</A>, <A HREF="#signal">signal</A>, <A
HREF="#variable">variable</A>, or file). (&#167;4.3.3, &#167;4.3.3.1)
<I>See also</I> <A HREF="#nonobject alias">nonobject alias</A>.<P>

<B>B.174 <A NAME="overloaded"> overloaded</A>:</B> Identifiers or <A
HREF="#enumeration literal">enumeration literals</A> that
denote two different <A HREF="#named entity">name
entities</A>. <A HREF="#enumeration literal">Enumeration literals</A>,
subprograms, and <A HREF="#predefined operators">predefined
operators</A> may be overloaded. At any
place where an overloaded <A
HREF="#enumeration literal">enumeration literal</A> occurs in the text
of a program, the <A HREF="#type">type</A> of the <A
HREF="#enumeration literal">enumeration literal</A> must be
determinable from the context. (&#167;2.1, &#167;2.3, &#167;2.3.1,
&#167;2.3.2, &#167;3.1.1)<P>

<B>B.175 <A NAME="parameter"> parameter</A>:</B> A <A
HREF="#constant">constant</A>, <A HREF="#signal">signal</A>, <A
HREF="#variable">variable</A>, or file declared in the <A
HREF="#interface list">interface list</A> of a
<A HREF="#subprogram specification">subprogram specification</A>.
The characteristics of the class of <A HREF="#object">objects</A>
to which a given parameter belongs are also
characteristics of the parameter. In addition,
a parameter has an associated <A
HREF="#mode">mode</A> that specifies the direction of data flow
allowed through the parameter. (&#167;2.1.1,
&#167;2.1.1.1, &#167;2.1.1.2, &#167;2.1.1.3, &#167;2.3, &#167;2.6)<P>

<B>B.176 <A NAME="parameter interface list"> parameter interface
list</A>:</B> An <A HREF="#interface list">interface list</A> that
declares the <A HREF="#parameter">parameters</A> for a subprogram. It
may contain interface <A HREF="#constant">constant</A> <A
HREF="#declaration">declarations</A>, interface <A
HREF="#signal">signal</A> <A HREF="#declaration">declarations</A>,
interface <A HREF="#variable">variable</A> <A
HREF="#declaration">declarations</A>, interface file <A
HREF="#declaration">declarations</A>, or any combination
thereof. (&#167;4.3.2.1)<P>

<B>B.177 <A NAME="parameter type profile"> parameter type
profile</A>:</B> Two <A HREF="#formal">formal parameter</A>
lists that have the same number of <A
HREF="#parameter">parameters</A>, and at each <A
HREF="#parameter">parameter</A> position the corresponding <A
HREF="#parameter">parameters</A> have the same base <A
HREF="#type">type</A>. (&#167;2.3)<P>

<B>B.178 <A NAME="parameter and result type profile"> parameter and
result type profile</A>:</B> Two subprograms that have the same <A
HREF="#parameter type profile">parameter type profile</A>, and either
both are functions with the same result base <A HREF="#type">type</A>,
or neither of the two is a function. (&#167;2.3)<P>

<B>B.179 <A NAME="parent"> parent</A>:</B> A process or a subprogram
that contains a procedure call statement for a given procedure or for
a parent of the given procedure. (&#167;2.2)<P>

<B>B.180 <A NAME="passive process"> passive process</A>:</B> A process
statement where neither the process itself, nor any procedure of which
the process is a <A HREF="#parent">parent</A>, contains a <A
HREF="#signal">signal</A> assignment statement. (&#167;9.2)<P>

<B>B.181 <A NAME="physical literal"> physical literal</A>:</B> A <A
HREF="#numeric literal">numeric literal</A> of a
<A HREF="#physical type">physical type</A>. (&#167;3.1.3)<P>

<B>B.182 <A NAME="physical type"> physical type</A>:</B> A numeric <A
HREF="#scalar type">scalar type</A> that is used to represent
measurements of some quantity. Each value of a
<A HREF="#physical type">physical type</A> has a position number that
is an integer value. Any value of a physical type is an integral multiple
of the primary unit of measurement for that
<A HREF="#type">type</A>. (&#167;3.1, &#167;3.1.3)<P>

<B>B.183 <A NAME="port"> port</A>:</B> A channel for dynamic
communication between a <A HREF="#block">block</A> and its
environment. A <A HREF="#signal">signal</A> declared in the <A
HREF="#interface list">interface list</A> of an
<A HREF="#entity declaration">entity declaration</A>, in the header of a <A
HREF="#block">block</A> statement, or in the
<A HREF="#interface list">interface list</A> of a component <A
HREF="#declaration">declaration</A>. In addition to the
characteristics of <A HREF="#signal">signals</A>, ports also have
an associated <A HREF="#mode">mode</A>; the <A HREF="#mode">mode</A>
constrains the directions of data flow allowed through the port.
(&#167;1.1.1.2, &#167;4.3.1.2)<P>

<B>B.184 <A NAME="port interface list"> port interface list</A>:</B>
An <A HREF="#interface list">interface list</A> that declares the
inputs and outputs of a <A HREF="#block">block</A>,
component, or <A HREF="#design entity">design entity</A>. It consists
entirely of interface <A HREF="#signal">signal</A> <A
HREF="#declaration">declarations</A>. (&#167;1.1.1, &#167;1.1.1.2,
&#167;4.3.2.1, &#167;4.3.2.2, &#167;9.1)<P>

<B>B.185 <A NAME="positional association"> positional
association</A>:</B> An <A HREF="#association element">association
element</A> that does not contain an explicit appearance of the <A
HREF="#formal">formal</A> <A HREF="#designator">designator</A>. An <A
HREF="#actual">actual</A> <A HREF="#designator">designator</A> at a
given position in an <A HREF="#association list">association list</A>
corresponds to the interface element at the same position in the <A
HREF="#interface list">interface list</A>. (&#167;4.3.2.2,
&#167;7.3.2)<P>

<B>B.186 <A NAME="postponed process"> postponed process</A>:</B> An
explicit or implicit process whose source
statement contains the reserved word <B>postponed</B>. When a postponed
process is resumed, it does not <A HREF="#execute">execute</A> until the final
<A HREF="#simulation cycle">simulation cycle</A> at the current modeled
time. Thus, a postponed process accesses the values of
<A HREF="#signal">signals</A> that are the
&quot;stable&quot; values at the current simulated
time. (&#167;9.2)<P>

<B>B.187 <A NAME="predefined operators"> predefined operators</A>:</B>
Implicitly defined operators that operate on the predefined <A
HREF="#type">types</A>. Every predefined operator is a
<A HREF="#pure function">pure function</A>. No predefined operators
have named <A HREF="#formal">formal</A> <A HREF="#parameter">parameters</A>;
therefore, <A HREF="#named association">named association</A> may not
be used when invoking a predefined operation. (&#167;7.2,
&#167;14.2)<P>

<B>B.188 <A NAME="primary"> primary</A>:</B> One of the elements
making up an <A HREF="#expression">expression</A>. Each <A
HREF="#primary">primary</A> has a value and a <A
HREF="#type">type</A>. (&#167;7.1)<P>

<B>B.189 <A NAME="projected output waveform"> projected output
waveform</A>:</B> A sequence of one or more <A
HREF="#transaction">transactions</A> representing the current and
projected future values of the <A
HREF="#driver">driver</A>. (&#167;12.6.1)<P>

<B>B.190 <A NAME="pulse rejection limit"> pulse rejection
limit</A>:</B> The threshold time limit for which a <A
HREF="#signal">signal</A> value whose duration is greater than the
limit will be propagated. A <A HREF="#pulse rejection limit">pulse
rejection limit</A> is specified by the reserved word <B>reject</B> in an
inertially delayed <A HREF="#signal">signal</A> assignment
statement. (&#167;8.4)<P>

<B>B.191 <A NAME="pure function"> pure function</A>:</B> A function
that returns the same value each time it is called with the same
values as <A HREF="#actual">actual</A> <A
HREF="#parameter">parameters</A>. An <A HREF="#impure function"><I>impure</I>
function</A> may return a different value each time it is called, even
when different calls have the same <A HREF="#actual">actual</A> <A
HREF="#parameter">parameter</A> values. (&#167;2.1)<P>

<B>B.192 <A NAME="quiet"> quiet</A>:</B> In a given <A
HREF="#simulation cycle">simulation cycle</A>, a <A
HREF="#signal">signal</A> that is not active. (&#167;12.6.2)<P>

<B>B.193 <A NAME="range"> range</A>:</B> A specified subset of values
of a <A HREF="#scalar type">scalar type</A>. (&#167;3.1) <I>See also</I> <A
HREF="#ascending range">ascending range</A>,
<A HREF="#belong (to a range)">belong (to a range)</A>,
<A HREF="#descending range">descending range</A>, <A HREF="#lower bound">
lower bound</A>, and <A HREF="#upper bound">upper bound</A>.<P>

<B>B.194 <A NAME="range constraint"> range constraint</A>:</B> A
construct that specifies the <A HREF="#range">range</A> of values in a
<A HREF="#type">type</A>. A <A HREF="#range constraint">range
constraint</A> is <I>compatible</I> with a <A HREF="#subtype">subtype</A> if
each bound of the <A HREF="#range">range</A> <A
HREF="#belong (to a subtype)">belong to a subtype</A> or if the <A
HREF="#range constraint">range constraint</A> defines a
<A HREF="#null range">null range</A>. The direction of a
<A HREF="#range constraint">range constraint</A> is the same as the
direction of its <A HREF="#range">range</A>. (&#167;3.1, &#167;3.1.2,
&#167;3.1.3, &#167;3.1.4)<P>

<B>B.195 <A NAME="read"> read</A>:</B> The value of an <A
HREF="#object">object</A> is said to be <I>read</I> when
its value is referenced or when certain of its <A
HREF="#attribute">attributes</A> are referenced. (&#167;4.3.2)<P>

<B>B.196 <A NAME="real literal"> real literal</A>:</B> An <A
HREF="#abstract literal">abstract literal</A> of the <A
HREF="#type">type</A> <A HREF="#universal_real">universal_real</A>
that contains a base point. (&#167;13.4)<P>

<B>B.197 <A NAME="record type"> record type</A>:</B> A <A
HREF="#composite type">composite type</A> whose values consist of
named elements. (&#167;3.2.2, &#167;7.3.2.1)<P>

<B>B.198 <A NAME="reference"> reference</A>:</B> Access to a <A
HREF="#named entity">named entity</A>. Every appearance of a <A
HREF="#designator">designator</A> (a <A HREF="#name">name</A>, <A
HREF="#character literal">character literal</A>, or operator symbol)
is a <A HREF="#reference">reference</A> to the
<A HREF="#named entity">named entity</A> denoted by the <A
HREF="#designator">designator</A>, unless the <A
HREF="#designator">designator</A> appears in a <A
HREF="#library">library</A> clause or use clause. (&#167;10.4,
&#167;11.2)<P>

<B>B.199 <A NAME="register"> register</A>:</B> A kind of <A
HREF="#guarded signal">guarded signal</A> that retains its last driven
value when all of its <A HREF="#driver">drivers</A> are turned
off. (&#167;4.3.1.2)<P>

<B>B.200 <A NAME="regular structure"> regular structure</A>:</B> <A
HREF="#instance">Instances</A> of one or more components arranged and
interconnected (via <A HREF="#signal">signals</A>) in a repetitive
way. Each <A HREF="#instance">instance</A> may have characteristics
that depend upon its position within the <A HREF="#group">group</A> of
<A HREF="#instance">instances</A>. Regular structures may be represented
through the use of the generate statement. (&#167;9.7)<P>

<B>B.201 <A NAME="resolution"> resolution</A>:</B> The process of
determining the <A HREF="#resolved value">resolved value</A> of a <A
HREF="#resolved signal">resolved signal</A> based on the values of
multiple <A HREF="#source">sources</A> for that <A
HREF="#signal">signal</A>. (&#167;2.4, &#167;4.3.1.2)<P>

<B>B.202 <A NAME="resolution function"> resolution function</A>:</B> A
user-defined function that computes the <A HREF="#resolved value">
resolved value</A> of a <A HREF="#resolved signal">resolved
signal</A>. (&#167;2.4, &#167;4.3.1.2)<P>

<B>B.203 <A NAME="resolution limit"> resolution limit</A>:</B> The
primary unit of <A HREF="#type">type</A> TIME (by
default, 1 femtosecond). Any TIME value whose absolute value is
smaller than this limit is truncated to zero (0) time
units. (&#167;3.1.3.1)<P>

<B>B.204 <A NAME="resolved signal"> resolved signal</A>:</B> A <A
HREF="#signal">signal</A> that has an associated
<A HREF="#resolution function">resolution function</A>. (&#167;4.3.1.2)<P>

<B>B.205 <A NAME="resolved value"> resolved value</A>:</B> The output
of the <A HREF="#resolution function">resolution function</A>
associated with the <A HREF="#resolved signal">resolved signal</A>,
which is determined as a function of the collection of <A
HREF="#inputs">inputs</A> from the multiple <A
HREF="#source">sources</A> of the <A
HREF="#signal">signal</A>. (&#167;2.4, &#167;4.3.1.2)<P>

<B>B.206 <A NAME="resource library"> resource library</A>:</B> A <A
HREF="#library">library</A> containing <A HREF="#library unit">library
units</A> that are referenced within the <A HREF="#design unit">design
unit</A> being analyzed. (&#167;11.2)<P>

<B>B.207 <A NAME="result subtype"> result subtype</A>:</B> The <A
HREF="#subtype">subtype</A> of the returned value of a
function. (&#167;2.1)<P>

<B>B.208 <A NAME="resume"> resume</A>:</B> The action of a wait
statement upon an enclosing process when the conditions on which the
wait statement is waiting are satisfied. If the enclosing process is a
<A HREF="#nonpostponed process">nonpostponed process</A>, the process
will subsequently <A HREF="#execute">execute</A> during the current <A
HREF="#simulation cycle">simulation cycle</A>. Otherwise, the process
is a <A HREF="#postponed process">postponed process</A>, which will <A
HREF="#execute">execute</A> during the final
<A HREF="#simulation cycle">simulation cycle</A> at the current simulated
time. (&#167;12.6.3)<P>

<B>B.209 <A NAME="right of"> right of</A>:</B> When a value V1 and a
value V2 <A HREF="#belong (to a range)">belong to a range</A> and
either the <A HREF="#range">range</A> is an
<A HREF="#ascending range">ascending range</A> and V2 is the predecessor
of V1, or the <A HREF="#range">range</A> is a
<A HREF="#descending range">descending
range</A> and V2 is the successor of V1. (&#167;14.1)<P>

<B>B.210 <A NAME="satisfy"> satisfy</A>:</B> A property of a value
with respect to some <A HREF="#constraint">constraint</A>. The value
is said to <I>satisfy</I> a <A
HREF="#constraint">constraint</A> if the value is in the subset of
values determined by the <A
HREF="#constraint">constraint</A>. (&#167;3, &#167;3.2.1.1)<P>

<B>B.211 <A NAME="scalar type"> scalar type</A>:</B> A <A
HREF="#type">type</A> whose values have no elements.
Scalar types consist of
<A HREF="#enumeration type">enumeration types</A>,
<A HREF="#integer type">integer types</A>,
<A HREF="#physical type">physical types</A>, and
<A HREF="#floating point types">floating point types</A>.
<A HREF="#enumeration type">Enumeration types</A> and
<A HREF="#integer type">integer types</A> are called
<A HREF="#discrete type">discrete types</A>.
<A HREF="#integer type">Integer types</A>,
<A HREF="#floating point types">floating point types</A>, and
<A HREF="#physical type">physical types</A> are called
<A HREF="#numeric type">numeric types</A>. All scalar types are
ordered; that is, all relational operators are predefined for their
values. (&#167;3, &#167;3.1)<P>

<B>B.212 <A NAME="scope"> scope</A>:</B> A portion of the text in
which a <A HREF="#declaration">declaration</A> may be <A
HREF="#visible">visible</A>. This portion is defined by visibility and
overloading rules. (&#167;10.2)<P>

<B>B.213 <A NAME="selected name"> selected name</A>:</B>
Syntactically, a <A HREF="#name">name</A> having a prefix and suffix
separated by a dot. Certain selected
names are used to denote record elements or <A HREF="#object">objects</A>
denoted by an <A HREF="#access value">access value</A>. The remaining
selected names are referred to as
<A HREF="#expanded name">expanded names</A>. (&#167;6.3, &#167;8.1)
<I>Also see</I> <A HREF="#expanded name">expanded name</A>.<P>

<B>B.214 <A NAME="sensitivity set"> sensitivity set</A>:</B> The set
of <A HREF="#signal">signals</A> to which a wait statement is
sensitive. The sensitivity set is given
explicitly in an on clause, or is implied by an <B>until</B>
clause. (&#167;8.1)<P>

<B>B.215 <A NAME="sequential statements">
sequential statements</A>:</B> Statements that <A HREF="#execute">
execute</A> in sequence in the order in which they appear.
Sequential statements are used for algorithmic
descriptions. (&#167;8)<P>

<B>B.216 <A NAME="short-circuit operation"> short-circuit
operation</A>:</B> An operation for which the right operand is
evaluated only if the left operand has a certain value. The
short-circuit operations are the
predefined logical operations <B>and</B>, <B>or</B>, <B>nand</B>,
and <B>nor</B> for operands of
<A HREF="#type">types</A> BIT and BOOLEAN. (&#167;7.2)<P>

<B>B.217 <A NAME="signal"> signal</A>:</B> An <A
HREF="#object">object</A> with a past history of values. A
signal may have multiple <A
HREF="#driver">drivers</A>, each with a <A HREF="#current value">
current value</A> and projected future values. The term
<I>signal</I> refers to <A HREF="#object">objects</A>
declared by signal <A HREF="#declaration">declarations</A>
or <A HREF="#port">port</A> <A HREF="#declaration">
declarations</A>. (&#167;4.3.1.2)<P>

<B>B.218 <A NAME="signal transform"> signal transform</A>:</B> A
sequential statement within a <A HREF="#statement transform">statement
transform</A> that determines which one of the alternative <A
HREF="#waveform">waveforms</A>, if any, is to be assigned to an output
<A HREF="#signal">signal</A>. A signal transform can be a
sequential <A HREF="#signal">signal</A> assignment statement, an
if statement, a case statement, or a null statement. (&#167;9.5)<P>

<B>B.219 <A NAME="simple name"> simple name</A>:</B> The identifier
associated with a <A HREF="#named entity">named entity</A>, either in
its own <A HREF="#declaration">declaration</A> or in an <A
HREF="#alias">alias</A> declaration. (&#167;6.2)<P>

<B>B.220 <A NAME="simulation cycle"> simulation cycle</A>:</B> One
iteration in the repetitive execution of the processes defined by
process statements in a <A HREF="#model">model</A>. The first
simulation cycle occurs after initialization. A simulation cycle can
be a <A HREF="#delta cycle">delta cycle</A> or a time-advance
cycle. (&#167;12.6.4)<P>

<B>B.221 <A NAME="single-object declaration"> single-object
declaration</A>:</B> An <A HREF="#object">object</A> <A
HREF="#declaration">declaration</A> whose identifier list contains a
single identifier; it is called a multiple-object declaration if
the identifier list contains two or more identifiers. (&#167;4.3.1)<P>

<B>B.222 <A NAME="slice"> slice</A>:</B> A one-dimensional array of a
sequence of consecutive elements of another one-dimensional
array. (&#167;6.5)<P>

<B>B.223 <A NAME="source"> source</A>:</B> A contributor to the value
of a <A HREF="#signal">signal</A>. A source can
be a <A HREF="#driver">driver</A> or <A HREF="#port">port</A> of a <A
HREF="#block">block</A> with which a <A HREF="#signal">signal</A> is
associated or a composite collection of sources. (&#167;4.3.1.2)<P>

<B>B.224 <A NAME="specification"> specification</A>:</B> A class of
construct that associates additional information with a <A
HREF="#named entity">named entity</A>. There are three kinds of
<A specifications: <A HREF="#attribute">attribute</A>
specifications, <A HREF="#configuration">configuration</A>
specifications, and disconnection specifications. (&#167;5)<P>

<B>B.225 <A NAME="statement transform"> statement transform</A>:</B>
The first sequential statement in the process equivalent to the
concurrent <A HREF="#signal">signal</A> assignment statement. The
statement transform defines the
actions of the concurrent <A HREF="#signal">signal</A> assignment
statement when it executes. The statement transform is followed by a
wait statement, which is the final statement in the equivalent
process. (&#167;9.5)<P>

<B>B.226 <A NAME="static"> static</A>:</B> <I>See</I> <A
HREF="#locally static expression">locally static</A> and <A
HREF="#globally static expression">globally static</A>.<P>

<B>B.227 <A NAME="static name"> static name</A>:</B> A <A
HREF="#name">name</A> in which every <A
HREF="#expression">expression</A> that appears as part of the <A
HREF="#name">name</A> (for example, as an index <A
HREF="#expression">expression</A>) is a <A HREF="#static">static</A>
<A HREF="#expression">expression</A> (if every <A HREF="#discrete range">
discrete range</A> that appears as part of the <A
HREF="#name">name</A> denotes a <A HREF="#static range">
static range</A> or <A HREF="#subtype">subtype</A> and if no
prefix within the <A HREF="#name">name</A> is either an <A
HREF="#object">object</A> or value of an <A HREF="#access type">access
type</A> or a function call). (&#167;6.1)<P>

<B>B.228 <A NAME="static range"> static range</A>:</B> A <A
HREF="#range">range</A> whose bounds are <A HREF="#static">static</A>
<A HREF="#expression">expressions</A>. (&#167;7.4)<P>

<B>B.229 <A NAME="static signal name"> static signal name</A>:</B> A
<A HREF="#static name">static name</A> that denotes a <A
HREF="#signal">signal</A>. (&#167;6.1)<P>

<B>B.230 <A NAME="static variable name"> static variable name</A>:</B>
A <A HREF="#static name">static name</A> that denotes a <A
HREF="#variable">variable</A>. (&#167;6.1)<P>

<B>B.231 <A NAME="string literal"> string literal</A>:</B> A sequence
of graphic characters, or possibly none, enclosed between two
quotation marks (&quot;). The <A HREF="#type">type</A> of a <A
HREF="#string literal">string literal</A> is determined from the
context. (&#167;7.3.1, &#167;13.6)<P>

<B>B.232 <A NAME="subaggregate"> subaggregate</A>:</B> An <A
HREF="#aggregate">aggregate</A> appearing as the <A
HREF="#expression">expression</A> in an element association within
another, multidimensional <A HREF="#array type">array</A> <A
HREF="#aggregate">aggregate</A>. The subaggregate is an
(<I>n</I>-1)-dimensional <A HREF="#array type">array</A>
<A HREF="#aggregate">aggregate</A>, where
<I>n</I> is the dimensionality of the outer <A HREF="#aggregate">aggregate</A>.
<A HREF="#aggregate">Aggregates</a> of multidimensional
<A HREF="#array type">arrays</A> are  expressed in row-major
(rightmost index varies fastest) order. (&#167;7.3.2.2)<P>

<B>B.233 <A NAME="subelement"> subelement</A>:</B> An element of
another element. Where other subelements are
excluded, the term <I>element</I> is used.(&#167;3)<P>

<B>B.234 <A NAME="subprogram specification"> subprogram
specification</A>:</B> Specifies the <A
HREF="#designator">designator</A> of the subprogram, any <A
HREF="#formal">formal</A> <A HREF="#parameter">parameters</A> of the
subprogram, and the result <A HREF="#type">type</A> for a function
subprogram. (&#167;2.1)<P>

<B>B.235 <A NAME="subtype"> subtype</A>:</B> A <A
HREF="#type">type</A> together with a <A
HREF="#constraint">constraint</A>. A value
<A HREF="#belong (to a subtype)">belongs to a subtype</A> of a
given <A HREF="#type">type</A>
if it belongs to the <A HREF="#type">type</A> and satisfies the <A
HREF="#constraint">constraint</A>; the given <A HREF="#type">type</A>
is called the <A HREF="#base type">base type</A> of the <A
HREF="#subtype">subtype</A>. A <A HREF="#type">type</A> is a <A
HREF="#subtype">subtype</A> of itself. Such a <A
HREF="#subtype">subtype</A> is said to be <I>unconstrained</I> because it
corresponds to a condition that imposes no restriction. (&#167;3)<P>

<B>B.236 <A NAME="suspend"> suspend</A>:</B> A process that stops
executing and waits for an <A HREF="#event">event</A> or for a time
period to elapse. (&#167;12.6.4)<P>

<B>B.237 <A NAME="timeout interval"> timeout interval</A>:</B> The
maximum time a process will be suspended, as specified by the timeout
period in the <B>until</B> clause of a wait statement. (&#167;8.1)<P>

<B>B.238 <A NAME="to the left of"> to the left of</A>:</B> <I>See</I> <A
HREF="#left of">left of</A>.<P>

<B>B.239 <A NAME="to the right of"> to the right of</A>:</B> <I>See</I> <A
HREF="#right of">right of</A>.<P>

<B>B.240 <A NAME="transaction"> transaction</A>:</B> A pair consisting
of a value and a time. The value represents a (current or) future
value of the <A HREF="#driver">driver</A>; the time represents the
relative delay before the value becomes the
<A HREF="#current value">current value</A>. (&#167;12.6.1)<P>

<B>B.241 <A NAME="transport delay"> transport delay</A>:</B> An
optional delay model for <A HREF="#signal">signal</A> assignment.
Transport delay is characteristic of hardware devices (such
as transmission lines) that exhibit nearly infinite frequency
response: any pulse is transmitted, no matter how short its
duration. (&#167;8.4) <I>See also</I> <A HREF="#inertial delay"> inertial
delay</A>.<P>

<A HREF="#Example16">[Example E.16]</A>

<p>

<B>B.242 <A NAME="type"> type</A>:</B> A set of values and a set of
operations. (&#167;3)<P>

<B>B.243 <A NAME="type conversion"> type conversion</A>:</B> An <A
HREF="#expression">expression</A> that converts the value of a
subexpression from one <A HREF="#type">type</A> to the designated type
of the type conversion. Associations in the form of a type conversion
are also allowed. These associations have functions and restrictions
similar to <A HREF="#conversion function">conversion functions</A>
but can be used in places where <A HREF="#conversion function">conversion
functions</A> cannot. In both cases (<A
HREF="#expression">expressions</A> and associations), the converted <A
HREF="#type">type</A> must be closely related to the <A
HREF="#designated type">designated type</A>. (&#167;4.3.2.2,
&#167;7.3.5) <I>See also</I> <A HREF="#conversion function">conversion
function</A> and <A HREF="#closely related types"> closely related
types</A>.<P>

<B>B.244 <A NAME="unaffected"> unaffected</A>:</B> A <A
HREF="#waveform">waveform</A> in a concurrent <A
HREF="#signal">signal</A> assignment statement that does not affect
the <A HREF="#driver">driver</A> of the target. (&#167;8.4,
&#167;9.5.1)<P>

<B>B.245 <A NAME="unassociated formal"> unassociated formal</A>:</B> A
<A HREF="#formal">formal</A> that is not associated with an <A
HREF="#actual">actual</A>. (&#167;5.2.1.2)<P>

<B>B.246 <A NAME="unconstrained subtype"> unconstrained
subtype</A>:</B> A <A HREF="#subtype">subtype</A> that corresponds to
a condition that imposes no restriction. (&#167;3, &#167;4.2)<P>

<B>B.247 <A NAME="unit name"> unit name</A>:</B> A <A
HREF="#name">name</A> defined by a unit <A
HREF="#declaration">declaration</A> (either the primary unit <A
HREF="#declaration">declaration</A> or a secondary unit <A
HREF="#declaration">declaration</A>) in a
<A HREF="#physical type">physical type</A> <A
HREF="#declaration">declaration</A>. (&#167;3.1.3)<P>

<B>B.248 <A NAME="universal_integer"> universal_integer</A>:</B> An <A
HREF="#anonymous">anonymous</A> predefined <A HREF="#integer type">
integer type</A> that is used for all
<A HREF="#integer literal">integer literals</A>. The position number
of an integer value is the corresponding value of the ...

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