VHDL Glossary | |
IEEE Std
1076-2002 - IEEE Standard VHDL Language Reference Manual, Copyright © 2006 by the
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| There are 265 entries in the glossary. | |
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| Term | Definition |
| Event | A change in the current value of a signal, which occurs when the signal is updated with its effective value. |
| Execute |
(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.
(B) When a process performs the actions specified by the algorithm described in its statement part. |
| Expanded name | 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. |
| Explicit ancestor |
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 member 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.
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| Explicit signal |
A signal, other than those defined by the predefined attributes 'DELAYED, 'QUIET, 'STABLE, or 'TRANSACTION, any implicit signal GUARD, or their slices, subelements, or slices of their subelements. A slice, subelement, or a slice of a subelement of an explicit signal is also an explicit signal.
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| Explicitly declared constant | A constant of a specified type that is declared by a constant declaration. |
| Explicitly declared object |
An object of a specified type that is declared by an object declaration. An object declaration is called a single-object declaration if its identifier list has a single identifier; it is called a multiple-object declaration if the identifier list has two or more identifiers.
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| Expression | A formula that defines the computation of a value. |
| Extend |
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 extend 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).
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| Extended digit | A lexical element that is either a digit or a letter. |
| External block | A top-level design entity that resides in a library and may be used as a component in other designs. |
| File type | 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. |
| Floating point types | 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. |
| Foreign subprogram | 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. |
| Formal | A formal port or formal generic of a design entity, a block statement, or a formal parameter of a subprogram. |
| Full declaration | 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. |
| Fully bound | A binding indication for the component instance implies an entity declaration and an architecture. |
| Generate parameter | 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. |
| Generic | 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. |
| Generic interface list | A list that defines local or formal generic constants. |
| Globally static expression | 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. |
| Globally static primary | 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. |
| Group | A named collection of named entities. Groups relate different named entities for the purposes not specified by the language. In particular, groups may be decorated with attributes. |
| Guard expression | A Boolean-valued expression associated with a block statement that controls assignments to guarded signals within the block. A guard expression defines an implicit signal GUARD that may be used to control the operation of certain statements within the block. |
| Guarded assignment | A concurrent signal assignment statement that includes the option guarded, which specifies that the signal assignment statement is executed when a signal GUARD changes from FALSE to TRUE, or when that signal has been TRUE and an event occurs on one of the signals referenced in the corresponding GUARD expression. The signal GUARD must be one of the implicitly declared GUARD signals associated with block statements that have guard expressions, or it must be an explicitly declared signal of type Boolean that is visible at the point of the concurrent signal assignment statement. |
| Guarded signal | A signal declared as a register or a bus. Such signals have special semantics when their drivers are updated from within guarded signal assignment statements. |
| Guarded target | A signal assignment target consisting only of guarded signals. An unguarded target is a target consisting only of unguarded signals. |
| Hidden | A declaration that is not directly visible. A declaration is hidden in its scope by a homograph of the declaration. |
| Homograph | A reflexive property of two declarations. Each of two declarations is said to be a homograph of the other if both declarations have the same identifier and overloading is allowed for at most one of the two. If overloading is allowed for both declarations, then each of the two is a homograph of the other if they have the same identifier, operator symbol, or character literal, as well as the same parameter and result type profile. |
| Identify | A property of a name appearing in an element association of an assignment target in the form of an aggregate. The name is said to identify a signal or variable and any subelements of that signal or variable. |
| Glossary & Definitions | |