Signal w_SUM : std_logic_vector(3 downto 0) Signal w_C : std_logic_vector(4 downto 0) - Carry
Signal w_P : std_logic_vector(3 downto 0) - Propagate Signal w_G : std_logic_vector(3 downto 0) - Generate O_result : out std_logic_vector(4 downto 0)Īrchitecture rtl of carry_lookahead_adder_4_bit is I_add2 : in std_logic_vector(3 downto 0) I_add1 : in std_logic_vector(3 downto 0) As long as inputs to the concatenation operator of the same type they can be concatenated together.
The output o_result is assigned using the ampersand (&) VHDL concatenation operator. This is because two N bit vectors added together can produce a result that is N+1 in size. Note that the carry lookahead adder output (o_result) is one bit larger than both of the two adder inputs. VHDL Implementation:Įxample 1: Four-Bit Carry Lookahead Adder in VHDL Therefore it is scalable for any input widths. The second example uses a generic that creates a carry look ahead adder that accepts as an input parameter the WIDTH of the inputs. The first contains a simple carry lookahead adder made up of four full adders (it can add together any four-bit inputs). There are two examples for each VHDL and Verilog shown below. Carry Lookahead Adder 4-bit Block Diagram
