Arithmetic operators in VHDL

Introduction

Arithmetic operators help you do math with numbers in your VHDL code. They let you add, subtract, multiply, and divide values.

When you want to add two signals or variables.

When you need to subtract one value from another.

When you want to multiply numbers for calculations.

When you need to divide one number by another.

When you want to calculate the remainder after division.

Syntax

VHDL

result := operand1 + operand2;  -- addition
result := operand1 - operand2;  -- subtraction
result := operand1 * operand2;  -- multiplication
result := operand1 / operand2;  -- division
result := operand1 mod operand2; -- modulus (remainder)

Operands must be of compatible numeric types like integer or unsigned.

Use 'mod' for remainder after division, not the '%' symbol.

Examples

Adds values of a and b and stores in sum.

VHDL

sum := a + b;

Subtracts y from x and stores in difference.

VHDL

difference := x - y;

Multiplies m and n and stores in product.

VHDL

product := m * n;

Calculates remainder of value divided by divisor.

VHDL

remainder := value mod divisor;

Sample Program

This program shows how to use arithmetic operators with integers in VHDL. It calculates sum, difference, product, quotient, and remainder of two signals and reports the results.

VHDL

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity ArithmeticDemo is
end ArithmeticDemo;

architecture Behavioral of ArithmeticDemo is
  signal a, b : integer := 10;
  signal sum, diff, prod, quot, rem : integer;
begin
  process
  begin
    sum <= a + b;
    diff <= a - b;
    prod <= a * b;
    quot <= a / b;
    rem <= a mod b;
    wait for 10 ns;
    report "Sum: " & integer'image(sum);
    report "Difference: " & integer'image(diff);
    report "Product: " & integer'image(prod);
    report "Quotient: " & integer'image(quot);
    report "Remainder: " & integer'image(rem);
    wait;
  end process;
end Behavioral;

Important Notes

Division by zero causes an error, so ensure divisor is not zero.

Use ieee.numeric_std package for arithmetic on unsigned and signed types.

Arithmetic operators work on integers and numeric types, not on std_logic directly.

Summary

Arithmetic operators perform basic math in VHDL.

Use +, -, *, / for add, subtract, multiply, divide.

Use mod to get the remainder after division.