1076_axb.html

basic exemple. Do an ADD of two 4 bits numbers

<p><b>B.70 designate:</b>  A property of access values that relates the value to some object when the access value is nonnull.  A nonnull access value is said to <i>designate</i> an object.  (&#167;  <a href = "1076_3.HTM#3.3"> 3.3 </a>  )
<p><b>B.71 designated subtype:</b>  For an access type, the subtype defined by the subtype indication of the access type definition.  (&#167;  <a href = "1076_3.HTM#3.3"> 3.3 </a>  )
<p><b>B.72 designated type:</b>  For an access type, the base type of the subtype defined by the subtype indication of the access type definition.  (&#167;  <a href = "1076_3.HTM#3.3"> 3.3 </a>  )
<p><b>B.73 designator:</b> 
<ul>
<p>a)  Syntax that forms part of an association element.  A formal designator specifies which formal parameter, port, or generic (or which subelement or slice of a parameter, port, or generic) is to be associated with an actual by the given association element.  An actual designator specifies which actual expression, signal, or variable is to be associated with a formal (or subelement or subelements of a formal).  An actual designator may also specify that the formal in the given association element is to be left unassociated (with an actual designator of <b>open</b>).  (&#167;  <a href = "1076_4.HTM#4.3.2.2"> 4.3.2.2 </a>  )
<p>b)  An identifier, character literal, or operator symbol that defines an alias for some other name.  (&#167;  <a href = "1076_4.HTM#4.3.3"> 4.3.3 </a>  )
<p>c)  A simple name that denotes a predefined or user-defined attribute in an attribute name, or a user-defined attribute in an attribute specification.(&#167;  <a href = "1076_5.HTM#5.1"> 5.1 </a>  , &#167;  <a href = "1076_6.HTM#6.6"> 6.6 </a>  )
<p>d)  An simple name, character literal, or operator symbol, and possibly a signature, that denotes a named entity in the entity name list of an attribute specification.  (&#167;  <a href = "1076_5.HTM#5.1"> 5.1 </a>  )
<p>e)  An identifier or operator symbol that defines the name of a subprogram.(&#167;  <a href = "1076_2.HTM#2.1"> 2.1 </a>  )
</ul>
<p><b>B.74 directly visible:</b>  A visible declaration that is not visible by selection.  A declaration is directly visible within its immediate scope,excluding any places where the declaration is hidden.  A declaration occurring immediately within the visible part of a package can be made directly visible by means of a use clause.  (<i>&#167;</i><i>  <a href = "1076_10.HTM#10.3"> 10.3 </a>  </i>, &#167;  <a href = "1076_10.HTM#10.4"> 10.4 </a>  ).  <i>See also</i> <b>visible</b>.
<p><b>B.75 discrete array:</b>  A one-dimensional array whose elements are of a discrete type.  (&#167;  <a href = "1076_7.HTM#7.2.3"> 7.2.3 </a>  )
<p><b>B.76 discrete range:</b>  A range whose bounds are of a discrete type.(&#167;  <a href = "1076_3.HTM#3.2.1"> 3.2.1 </a>  , &#167;  <a href = "1076_3.HTM#3.2.1.1"> 3.2.1.1 </a>  )
<p><b>B.77 discrete type:</b>  An enumeration type or an integer type.  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;  <a href = "1076_3.HTM#3.1"> 3.1 </a>  )
<p><b>B.78 driver:</b>   A container for a projected output waveform of a signal.  The value of the signal is a function of the current values of its drivers.  Each process that assigns to a given signal implicitly contains a driver for that signal.  A signal assignment statement affects only the associated driver(s).  (&#167;  <a href = "1076_12.HTM#12.4.4"> 12.4.4 </a>  , <i></i><i>&#167;</i><i>  <a href = "1076_12.HTM#12.6.1"> 12.6.1 </a>  </i><i>,</i> &#167;  <a href = "1076_12.HTM#12.6.2"> 12.6.2 </a>  , &#167;  <a href = "1076_12.HTM#12.6.3"> 12.6.3 </a>  )
<p><b>B.79 driving value:</b>  The value a signal provides as a source of other signals.  (&#167;  <a href = "1076_12.HTM#12.6.2"> 12.6.2 </a>  )
<p><b>B.80 effective value:</b>  The value obtained by evaluating a reference to the signal within an expression.  (&#167;  <a href = "1076_12.HTM#12.6.2"> 12.6.2 </a>  )
<p><b>B.81 elaboration:</b>  The process by which a declaration achieves its effect.  Prior to the completion of its elaboration (including before the elaboration), a declaration is not yet elaborated.  (&#167;12)
<p><b>B.82 element:</b>  A constituent of a composite type.  (&#167;3)  <i>See also</i> <b>subelement</b>.
<p><b>B.83 entity declaration:</b>  A definition of the interface between a given design entity and the environment in which it is used.  It may also specify declarations and statements that are part of the design entity.  A given entity declaration may be shared by many design entities, each of which has a different architecture.  Thus, an entity declaration can potentially represent a class of design entities, each with the same interface.  (<i>&#167;</i><i>1</i>, &#167;  <a href = "1076_1.HTM#1.1"> 1.1 </a>  )
<p><b>B.84 enumeration literal:</b>  A literal of an enumeration type.  An enumeration literal may be either an identifier or a character literal.(<i>&#167;</i>  <a href = "1076_3.HTM#3.1.1"> 3.1.1 </a>  , &#167;  <a href = "1076_7.HTM#7.3.1"> 7.3.1 </a>  )
<p><b>B.85 enumeration type:  </b>A type whose values are defined by listing(enumerating) them.  The values of the type are represented by enumeration literals.  (<i>&#167;</i><i>  <a href = "1076_3.HTM#3.1"> 3.1 </a>  </i>, &#167;  <a href = "1076_3.HTM#3.1.1"> 3.1.1 </a>  )
<p><b>B.86 error:</b>  A condition that makes the source description illegal.  If an error is detected at the time of analysis of a design unit, it prevents the creation of a library unit for the given design unit.  A run-time error causes simulation to terminate.  (&#167;  <a href = "1076_11.HTM#11.4"> 11.4 </a>  )
<p><b>B.87 erroneous:</b>  An error condition that cannot always be detected.(&#167;  <a href = "1076_2.HTM#2.1.1.1"> 2.1.1.1 </a>  , &#167;  <a href = "1076_2.HTM#2.2"> 2.2 </a>  )
<p><b>B.88 event:</b>  A change in the current value of a signal, which occurs when the signal is updated with its effective value.  (&#167;  <a href = "1076_12.HTM#12.6.2"> 12.6.2 </a>  )
<p><b>B.89 execute:</b>  
<ul>
<p>a)  When first the design hierarchy of a model is elaborated, then its nets are initialized, and finally simulation proceeds with repetitive execution of the simulation cycle, during which processes are executed and nets are updated.  
<p>b)  When a process performs the actions specified by the algorithm described in its statement part.  (&#167;12, &#167;  <a href = "1076_12.HTM#12.6"> 12.6 </a>  )
</ul>
<p><b>B.90 expanded name:</b>  A selected name (in the syntactic sense) that denotes one or all of the primary units in a library or any named entity within a primary unit.  (<i>&#167;</i>  <a href = "1076_6.HTM#6.3"> 6.3 </a>  , &#167;  <a href = "1076_8.HTM#8.1"> 8.1 </a>  )  <i>See also</i> <b>selected name</b>.
<p><b>B.91 explicit ancestor:</b> The parent of the implicit signal that is defined by the predefined attributes 'DELAYED, 'QUIET, 'STABLE, or 'TRANSACTION.  It is determined using the prefix of the attribute.  If the prefix denotes an explicit signal or a slice or subelement (or slice thereof),then that is the explicit ancestor of the implicit signal.  If the prefix is one of the implicit signals defined by the predefined attributes 'DELAYED,'QUIET, 'STABLE, or 'TRANSACTION, this rule is applied recursively.  If the prefix is an implicit signal GUARD, the signal has no explicit ancestor.(&#167;  <a href = "1076_2.HTM#2.2"> 2.2 </a>  )
<p><b>B.92 explicit signal:</b>  A signal defined by the predefined attributes 'DELAYED, 'QUIET, 'STABLE, or 'TRANSACTION.  (&#167;  <a href = "1076_2.HTM#2.2"> 2.2 </a>  )
<p><b>B.93 explicitly declared constant:</b>  A constant of a specified type that is declared by a constant declaration.  (&#167;  <a href = "1076_4.HTM#4.3.1.1"> 4.3.1.1 </a>  )
<p><b>B.94 explicitly declared object:</b>  An object of a specified type that is declared by an object declaration.  An object declaration is called a <i>single-object declaration</i> 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;  <a href = "1076_4.HTM#4.3"> 4.3 </a>  , <i>&#167;</i>  <a href = "1076_4.HTM#4.3.1"> 4.3.1 </a>  )  <i>See also</i> <b>implicitly declared object</b>.
<p><b>B.95 expression:</b>  A formula that defines the computation of a value.(&#167;  <a href = "1076_7.HTM#7.1"> 7.1 </a>  )
<p><b>B.96 extend:</b>   A property of source text forming a declarative region with disjoint parts.  In a declarative region with disjoint parts, if a portion of text is said to <i>extend</i> from some specific point of a declarative region to the end of the region, then this portion is the corresponding subset of the declarative region (and does not include intermediate declarative items between an interface declaration and a corresponding body declaration).(&#167;  <a href = "1076_10.HTM#10.1"> 10.1 </a>  )
<p><b>B.97 extended digit:</b>  A lexical element that is either a digit or a letter.  (&#167;  <a href = "1076_13.HTM#13.4.2"> 13.4.2 </a>  )
<p><b>B.98 external block:</b>  A top-level design entity that resides in a library and may be used as a component in other designs.  (&#167;1)
<p><b>B.99 file type:  </b>A type that provides access to objects containing a sequence of values of a given type.  File types are typically used to access files in the host system environment.  The value of a file object is the sequence of values contained in the host system file.  (&#167;3, <i>&#167;</i>  <a href = "1076_3.HTM#3.4"> 3.4 </a>  )
<p><b>B.100 floating point types:</b>  A discrete scalar type whose values approximate real numbers.  The representation of a floating point type includes a minimum of six decimal digits of precision.  (&#167;  <a href = "1076_3.HTM#3.1"> 3.1 </a>  , &#167;  <a href = "1076_3.HTM#3.1.4"> 3.1.4 </a>  )
<p><b>B.101 foreign subprogram:  </b>A subprogram that is decorated with the attribute 'FOREIGN, defined in package STANDARD.  The STRING value of the attribute may specify implementation-dependent information about the foreign subprogram.  Foreign subprograms may have non-VHDL implementations.  An implementation may place restrictions on the allowable modes, classes, and types of the formal parameters to a foreign subprogram, such as constraints on the number and allowable order of the parameters.  (&#167;  <a href = "1076_2.HTM#2.2"> 2.2 </a>  )
<p><b>B.102 formal: </b>A formal port or formal generic of a design entity, a block statement, or a formal parameter of a subprogram.  (<i>&#167;</i>  <a href = "1076_2.HTM#2.1.1"> 2.1.1 </a>  , <i>&#167;</i>  <a href = "1076_4.HTM#4.3.2.2"> 4.3.2.2 </a>  , <i>&#167;</i>  <a href = "1076_5.HTM#5.2.1.2"> 5.2.1.2 </a>  , &#167;  <a href = "1076_9.HTM#9.1"> 9.1 </a>  )
<p><b>B.103 full declaration: </b> A constant declaration occurring in a package body with the same identifier as that of a deferred constant declaration in the corresponding package declaration.  A full type declaration is a type declaration corresponding to an incomplete type declaration.  (&#167;  <a href = "1076_2.HTM#2.6"> 2.6 </a>  )
<p><b>B.104 fully bound:</b>  A binding indication for the component instance implies an entity interface and an architecture.  (&#167;  <a href = "1076_5.HTM#5.2.1.1"> 5.2.1.1 </a>  )
<p><b>B.105 generate parameter: </b>A constant object whose type is the base type of the discrete range of a generate parameter specification.  A generate parameter is declared by a generate statement.  (&#167;  <a href = "1076_9.HTM#9.7"> 9.7 </a>  )
<p><b>B.106 generic:</b>  An interface constant declared in the block header of a block statement, a component declaration, or an entity declaration.  Generics provide a channel for static information to be communicated to a block from its environment.  Unlike constants, however, the value of a generic can be supplied externally, either in a component instantiation statement or in a configuration specification.  (&#167;  <a href = "1076_1.HTM#1.1.1.1"> 1.1.1.1 </a>  )
<p><b>B.107 generic interface list:</b> A list that defines local or formal generic constants.  (&#167;  <a href = "1076_1.HTM#1.1.1.1"> 1.1.1.1 </a>  , &#167;  <a href = "1076_4.HTM#4.3.2.1"> 4.3.2.1 </a>  )
<p><b>B.108 globally static expression:</b>  An expression that can be evaluated as soon as the design hierarchy in which it appears is elaborated.  A locally static expression is also globally static unless the expression appears in a dynamically elaborated context.  (&#167;  <a href = "1076_7.HTM#7.4"> 7.4 </a>  )
<p><b>B.109 globally static primary:</b>  A primary whose value can be determined during the elaboration of its complete context and that does not thereafter change.  Globally static primaries can only appear within statically elaborated contexts. (&#167;  <a href = "1076_7.HTM#7.4.2"> 7.4.2 </a>  )