VHDL Programming

Data Types 79

Enumerated

Real

Integer

Physical

Scalar

Array Record

Composite

File Access

Figure 4-1 Types
VHDL Data Types
Diagram.

A type_markconstruct encompasses a wide range of methods for spec-

ifying a type. It can be anything from an enumeration of all of the values

of a type to a complex record structure. In the next few sections, type

marks are examined. All of the scoping rules that were defined for signals

and variables apply to type declarations also.

Figure 4-1 is a diagram showing the types available in VHDL. The four

broad categories are scalar types, composite types, access types, and file

types. Scalar types include all of the simple types such as integer and real.

Composite types include arrays and records. Access types are the equiv-

alent of pointers in typical programming languages. Finally, file types give

the designer the ability to declare file objects with designer-defined file

types.

Scalar Types

Scalar types describe objects that can hold, at most, one value at a time.

The type itself can contain multiple values, but an object that is declared