VHDL Tutorial

Scalar type in VHDL
Introduction
Fundamental concepts
Modelling concepts
Elements of behaviour
Elements of structure
Analysis elaboration
Lexical elements
Identifiers
Numbers
Characters and strings 
Syntax descriptions
Constants and variables
Scalar type

Integer types
Floating point types
Time type
Enumeration types
Character types
Boolean type 
Bits type
Standard logic
Sequential statements
Case statements
Loop and exit statements
Assertion statements
Array types & array operations
Architecture bodies
Entity declarations
Behavioral descriptions 
Wait statements
Delta delays
Process statements
Conditional signal assignment 
Selected signal assigment
Structural descriptions
Library and library clauses
Procedures
Procedure parameters
Signal parameters
Default values
Unconstrained array parameter
Functions
Package declarations and bodies
Subprograms in package
Use clauses
Resolved signals and subtypes
Resolved signals and ports
Parameterizing behavior
Parameterizing structure
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       Scalar Types

 

A scalar type is one whose values are indivisible In this section, we review VHDLís predefined scalar types.   We will also show how to define new enumeration types.

 

Subtypes

 

In many models, we want to declare objects that should only take on a restricted range

of values.  We do so by first declaring a subtype, which defines a restricted set of val- ues from a base type The simplified syntax rules for a subtype declaration are

 

subtype_declaration subtype identifier is subtype_indication ;

subtype_indication

type_mark range simple_expression ( to I downto ) simple_expression

 

We will look at other forms of subtype indications later.  The subtype declaration defines the identifier as a subtype of the base type specified by the type mark, with the range constraint restricting the values for the subtype.

 

 

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