Data Types

A data type appears in a declaration to identify the type used at that point. There are four classes of types in VHDL:

• Scalar types: represent a single numeric value, or in the case of enumerated types, an enumeration value.
  The standard types that fall into this class are:
  • Enumeration
  • Floating Point
  • Integer
  • Physical
• Composite types: represent a collection of values.
  The standard types that fall into this call are:
  • Array
  • Record
• Access type provide access to objects, equivalent to pointers in software programming languages.
• File type reference objects (typically disk files) that contain a sequence of values.

You can define your own type based on one of the classes mentioned above, or constrain an existing type with the subtype keyword.