Verilog code to implement a 4-bit ripple carry adder circuit.

Here’s an example Verilog code to implement a 4-bit ripple carry adder circuit:

module ripple_carry_adder (output reg [3:0] sum, output reg carry_out, input [3:0] a, b, input carry_in);

    always @(a, b, carry_in) begin
        reg carry;
        sum[0] = a[0] ^ b[0] ^ carry_in;
        carry = (a[0] & b[0]) | (a[0] & carry_in) | (b[0] & carry_in);
        sum[1] = a[1] ^ b[1] ^ carry;
        carry = (a[1] & b[1]) | (a[1] & carry) | (b[1] & carry);
        sum[2] = a[2] ^ b[2] ^ carry;
        carry = (a[2] & b[2]) | (a[2] & carry) | (b[2] & carry);
        sum[3] = a[3] ^ b[3] ^ carry;
        carry_out = (a[3] & b[3]) | (a[3] & carry) | (b[3] & carry);
    end

endmodule

This code defines a module called “ripple_carry_adder” that implements a 4-bit ripple carry adder. The output “sum” is a registered output that represents the sum of the two 4-bit inputs “a” and “b”. The output “carry_out” is a registered output that represents the carry-out of the addition operation. The input “carry_in” is the carry-in to the addition operation.

The “always @(a, b, carry_in)” block is a combinational logic block that updates the “sum” and “carry_out” outputs based on the inputs. The adder operates by performing a full adder operation on each bit of the two input vectors, starting with the least significant bit and propagating the carry to the next bit.

The “carry” variable is a temporary storage for the carry-out of each full adder operation. The first full adder operation takes the least significant bits of “a” and “b” and the carry-in, and calculates the sum and carry-out. The sum is then assigned to the least significant bit of “sum”, and the carry-out is stored in the “carry” variable. The process is repeated for the next three bits, with the “carry” variable holding the carry-out from the previous bit. Finally, the carry-out of the last full adder operation is assigned to the “carry_out” output.

Note that this Verilog code assumes that the “a” and “b” inputs, “sum” and “carry_out” outputs, and the “carry_in” signal are all 1-bit signals. If you want to use multi-bit signals, you would need to modify the code accordingly.