This information lists the inferred structure. Values are passed between statements by signals an assignment to a signal ( p p p p bit Concurrent statements (like netlists and classic PLD programming languages) are evaluated independently of the order in which they appear. Most of the examples in this guide use a single entity-architecture pair.Īn architecture contains concurrent statements. A design may contain any number of package, entity and architecture statements. An entity contains declarations of the design I/O, and an architecture contains the description of the design. The basic organization of a VHDL design description is shown below:Ī package is an optional statement for shared declarations. In the example above, the name "sum" is a user-defined identifier. Reserved words cannot be used as user-defined identifiers. Regular plain type represents a user-definable identifier or another VHDL construct. In the example above, entity, is, port, in, out, and end are all reserved words In examples, bold type indicates a reserved word. Port (clk, reset: in bit sum: out integer) VHDL reserved words in both the text and the examples are bold, for example : In this reference, examples are all lowercase.
VHDL is not case-sensitive, so a design description can contain UPPERCASE or lowercase text.
This version is basically a superset of the previous standard VHDL'87. The VHDL Synthesizer uses the VHDL'93 version of VHDL. The exceptions and constraints on the Synthesizer's VHDL support are listed in the topics 'Unsupported Constructs', 'Ignored Constructs', and 'Constrained Constructs'. the file operations in the package "textio", for example.
The VHDL Synthesis engine supports most of the VHDL language, however, some sections of the language have meanings that are unclear in the context of logic design rather it introduces enough of the language to enable useful design.
Modelsim altera signal assignment full#
This reference does not attempt to describe the full language VHDL is a large language and it provides many features. It contains the features of a conventional programming language, a classical PLD programming language, and a netlist, as well as design management features. VHDL is a hardware description language (HDL). The following content has been imported from Legacy Help systems and is in the process of being checked for accuracy.