Get Knowledge of Operators in VHDL with Examples

VHDL has wide range of Operators, which can be grouped into following

• Logical Operators
• Relational Operators
• Shift Operators.
• Miscellaneous Operators

1. Logical Operators 
• These operators can be applied on variable and signals of std_logic, bit and boolean data types.
• These can't applied to any user defined data types.
• There are seven logical operators : And, Or, Nand, Nor, Xor, Xnor and Not
  a = "0011", b="1010"
  y_and <= a and b; so y_and will be "0010"
  y_or <= a or b; then y_or will be "1001"
  y_nand <= a nand b; then y_nand will be "1101"
  y_nor <= a nor b; then y_nor will be "0110"
  y_xor <= a xor b; then y_xor will be "1001"
  y_xnor <= a xnor b; then y_xnor will be "0110"
  y_not <= not a; then y_not will be "1100"
2. Relational Operators
• These operators are used in expression when it is necessary to compare the values of objects.
• Values returned by such expression is always Boolean type. It returns True if condition in given relation is met otherwise False is returned.
• There are six relational operators. equal to(=), not equal to(/=), less than(<), less than or equal to(<=), greater than(>), greater than or equal to(>=).
  a = "0101", b = "1010"
  a = b; --> False
  a /= b; --> True
  a < b; --> True
  a <= b; --> True
  a > b; --> False
  a >= b; --> False
3. Shift Operators
• There are total three types of shift operators
• Logical.
• Arithmetic.
• Rotate.
• Find out more about Shift Operators here.
4. Miscellaneous Operators
• There are Addition(+), Subtraction(-), Concatenation(&), Multiplication(*), Division(/), Reminder(rem), Modulus(mod), Absolute(abs) and Exponentiation(**) operators used in VHDL.
• a = "1010", b = "0011"
  y_addition <= a + b; then y_addition will be "1101"
  y_sub <= a - b; then y_sub will be "0111"
  y_con <= a & b; then y_con will be "10100011". Join a and b.
  y_mul <= a * b; then y_mul will be "00011110"
  y_div <= a / b; then y_div will be "0011"
  c1 <= 3, d1 <= 8, c2 <= -3, d2 <= -8
  y_exp <= c1 ** d1; then y_exp will be 6561.
  y_rem <= d1 rem c1, then y_rem will be 5.
  y_rem <= d1 rem c2, then y_rem will be 5.
  y_rem <= d2 rem c1, then y_rem will be -5.
  y_rem <= d2 rem c2, then y_rem will be -5.
  y_mod <= d1 mod c1, then y_rem will be 5.
  y_mod <= d1 mod c2, then y_rem will be -5.
  y_mod <= d2 mod c1, then y_rem will be 5.
  y_mod <= d2 mod c2, then y_rem will be -5.