What Is Natural Data Type in VHDL?


Angela Bailey

What Is Natural Data Type in VHDL?

The natural data type in VHDL is a numeric data type that represents non-negative integers. It is often used when dealing with countable quantities or values that cannot be negative. In this article, we will explore the natural data type in VHDL and understand its features and usage.

The Natural Data Type

The natural data type is defined in the IEEE standard package “numeric_std” and is part of the VHDL language. It is a subtype of the integer data type, which means it inherits all the properties and operations of integers but with certain restrictions.

Features of Natural Data Type

The following are some key features of the natural data type:

  • Non-Negative Values: The natural data type allows only non-negative values, starting from zero. Negative values are not allowed.
  • Range: The range of the natural data type depends on the implementation. It can vary from system to system but generally supports a wide range of non-negative integers.
  • Arithmetic Operations: Arithmetic operations like addition, subtraction, multiplication, and division can be performed on natural numbers.
  • Comparison Operations: Comparison operators like equal to (=), not equal to (/=), greater than (>), less than (<), etc., can be used with natural numbers.

Usage of Natural Data Type

The natural data type is commonly used in VHDL for various purposes:

  • Counters: Counters are frequently implemented using the natural data type because they involve counting events or occurrences that cannot be negative.
  • Indexes: The natural data type is often used for indexing arrays or accessing specific elements in a collection.
  • Loop Iterations: When designing loops, the natural data type can be used to control the number of iterations.


Let’s look at an example to understand the usage of the natural data type:

architecture Behavioral of Example is
  signal counter : natural := 0;
    if rising_edge(clk) then
      if reset = '1' then
        counter <= 0; -- Reset the counter to zero
        counter <= counter + 1; -- Increment the counter by one
      end if;
    end if;
  end process;
end architecture;

In this example, we have a simple behavioral VHDL code that implements a counter using the natural data type. The counter starts at zero and increments by one on each clock cycle, except when a reset signal is asserted.


The natural data type in VHDL provides a convenient way to work with non-negative integers. It offers various features and can be used for counting, indexing, and loop iterations. Understanding its properties and usage is essential for writing efficient and reliable VHDL code.

Remember to always consider the range limitations of the natural data type in your design and ensure that it aligns with your system requirements. Using it correctly can help create robust and error-free designs in VHDL.

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