Array

A data type which consists of a vector or a multi-dimensional set of values of the same base type. Can be used to describe RAMs, ROMs, FIFOs, or any regular multi-dimensional structure.

Syntax ( Key to Notation )

type NewName is {unconstrained}
  array (IndexTypeName range <>, ...) of DataType;

type NewName is {constrained}
  array (Range, ...) of DataType;

Where

See Declaration

Rules

• The base type DataType must not be an unconstrained array type.
• A signal or variable cannot be an unconstrained array, unless it is a generic, port or parameter.

Synthesis

Some synthesis tools do not support multi-dimensional arrays, only support arrays of bits or arrays of vectors, or do not permit ports to be arrays of arrays.

Tips

• Large arrays should be variables or constants, rather than signals. A large signal array would be inefficient for simulation.
• The values within an array can be read or written using an indexed name or a slice name.

Example

subtype Word is Std_logic_vector(15 downto 0);
type Mem is array (0 to 2**12-1) of Word;
variable Memory: Mem := (others => Word'(others=>'U'));
...
if MemoryRead then
  Data <= Memory(To_Integer(Address));
elsif MemoryWrite then
  Memory(To_Integer(Address)) := Data;
end if;

See Also

Range, Name, String, Type

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