Click here to return to the VHDL Reference Guide. (last edit: 24. september 2012)

Name

Any VHDL "thing" is identified by its name. A selected name is commonly used to pick an item out of a library or package. An indexed name is used to pick an individual item out of an array. A slice name is used to pick out part of an array.

Syntax

  Identifier
  \ExtendedIdentifier\
  "Operator"
  Name.Name. ...                                 {selected name}
  Name(Expression, ...)                          {indexed name}
  Name(Range)                                    {slice name}
  AttributeName

Rules

An identifier consists of letters, digits and underscores. The first character must be a letter. The last character must not be an underscore, nor can a name contain two adjacent underscores.
An extended identifier consists of any printable characters.
One name cannot have more than one meaning at any particular point in the VHDL text, with the exception of procedures, functions and enumeration literals, which may be overloaded. Inner declarations of names hide outer declarations.

Things to remember

The direction (i.e. to or downto) of the range in a slice name must be consistent with the subtype of the thing being sliced; otherwise it is a null range, i.e. an array of length zero.

Tips

Generally, choose names which are meaningful to the reader. However, this is more important for global names than for local names. For example, G0123 is a bad name for a global reset signal, but I is an acceptable name for a loop parameter.

Example

  A_99_Z                                         -- Identifier
  \$%^&*()\                                      -- Extended identifer
  "+"                                            -- Operator
  IEEE.STD_LOGIC_1164."nand"                     -- Selected name
  RecordVariable.ElementName                     -- Selected name
  Vector(7)                                      -- Indexed name
  Matrix(I, J, K)                                -- Indexed name
  Vector(23 downto 16)                           -- Slice name
  Vector(J to K)                                 -- Slice name
  Clock'EVENT                                    -- Attribute name

See Also

Attribute Name, Operator, Expression, Range, Array, Record