VHDL Glossary | |
IEEE Std
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| There are 265 entries in the glossary. | |
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| Term | Definition |
| Subaggregate | An aggregate appearing as the expression in an element association within another, multidimensional array aggregate. The subaggregate is an (n–1)-dimensional array aggregate, where n is the dimensionality of the outer aggregate. Aggregates of multidimensional arrays are expressed in row-major (right-most index varies fastest) order. |
| Subelement | An element of another element. Where other subelements are excluded, the term element is used. |
| Subprogram specification | Specifies the designator of the subprogram, any formal parameters of the subprogram, and the result type for a function subprogram. |
| Subtype | A type together with a constraint. A value belongs to a subtype of a given type if it belongs to the type and satisfies the constraint; the given type is called the base type of the subtype. A type is a subtype of itself. Such a subtype is said to be unconstrained because it corresponds to a condition that imposes no restriction. |
| Suspend | A process that stops executing and waits for an event or for a time period to elapse. |
| Target library | A library containing the design unit in which a given component is declared. The target library is used to determine the visible entity declaration under certain circumstances for a default binding indication. |
| Timeout interval | The maximum time a process will be suspended, as specified by the timeout period in the until clause of a wait statement. |
| Transaction | A pair consisting of a value and a time. The value represents a (current or) future value of the driver; the time represents the relative delay before the value becomes the current value. |
| Transport delay | An optional delay model for signal 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. |
| Type | A set of values and a set of operations. |
| Type conversion | An expression that converts the value of a subexpression from one type 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 conversion functions but can be used in places where conversion functions cannot. In both cases (expressions and associations), the converted type must be closely related to the designated type. |
| Unaffected | A waveform in a concurrent signal assignment statement that does not affect the driver of the target. |
| Unassociated formal | A formal that is not associated with an actual. |
| Unconstrained subtype | A subtype that corresponds to a condition that imposes no restriction. |
| Unit name | A name defined by a unit declaration (either the primary unit declaration or a secondary unit declaration) in a physical type declaration. |
| Universal_integer | An anonymous predefined integer type that is used for all integer literals. The position number of an integer value is the corresponding value of the type universal_integer. |
| Universal_real | An anonymous predefined type that is used for literals of floating point types. Other floating point types have no literals. However, for each floating point type there exists an implicit conversion that converts a value of type universal_real into the corresponding value (if any) of the floating point type. |
| Update | An action on the value of a signal, variable, or file. The value of a signal is said to be updated when the signal appears as the target (or a component of the target) of a signal assignment statement (indirectly); when it is associated with an interface object of mode out, buffer, inout, or linkage; or when one of its subelements (individually or as part of a slice) is updated. The value of a signal is also said to be updated when it is a subelement or slice of a resolved signal, and the resolved signal is updated. The value of a variable is said to be updated when the variable appears as the target (or a component of the target) of a variable assignment statement (indirectly), when it is associated with an interface object of mode out or linkage, or when one of its subelements (individually or as part of a slice) is updated. The value of a file is said to be updated when a WRITE operation is performed on the file object. |
| Upper bound | For a range L to R or L downto R, the larger of L and R. |
| Variable | An object with a single current value. |
| Visible | When the declaration of an identifier defines a possible meaning of an occurrence of the identifier used in the declaration. A visible declaration is visible by selection (for example, by using an expanded name) or directly visible (for example, by using a simple name). |
| Visible entity declaration | The entity declaration selected for default binding in the absence of explicit binding information for a given component instance. |
| Waveform | A series of transactions, each of which represents a future value of the driver of a signal. The transactions in a waveform are ordered with respect to time, so that one transaction appears before another if the first represents a value that will occur sooner than the value represented by the other. |
| Whitespace character | A space, a nonbreaking space, or a horizontal tabulation character (SP, NBSP, or HT). |
| Working library | A design library into which the library unit resulting from the analysis of a design unit is placed. |
| Glossary & Definitions | |