create procedure SaveTest
   @Id numeric(18,0),
   @Value varchar(256),
   @IdNew numeric(18,0) output
as
begin
   declare
     @ReturnValue int

   if(not exists (select 1 from Test where Id=@Id))
     begin
       insert into Test
       (Value)
       values
       (@Value)

       set @ReturnValue=@@error
       set @IdNew=scope_identity()
     end
   else
     begin
       update
         Test
       set
         Value=@Value
       where
         Id=@id

       set @ReturnValue=@@error
       set @IdNew=@Id
     end

    return(@ReturnValue)
end

GO

protected void Button1_Click(object sender, EventArgs e)
        {
            string ConnectionString = ConfigurationSettings.AppSettings["ConnectionString"];
            SqlConnection connection = new SqlConnection(ConnectionString);

            connection.Open();
            SqlCommand command = new SqlCommand("SaveTest", connection);
            command.CommandType = CommandType.StoredProcedure;
            SqlCommandBuilder.DeriveParameters(command);
            command.Parameters["@Id"].Value = Int32.Parse(Id.Text);
            command.Parameters["@Value"].Value = Value.Text;
            command.Parameters["@IdNew"].Direction = ParameterDirection.Output;
            command.ExecuteNonQuery();
            if ((int)command.Parameters["@RETURN_VALUE"].Value == 0)
            {
              IdNew.Text = Convert.ToString(command.Parameters["@IdNew"].Value);
               
            }

            else
            {
                
            }
            connection.Close();

command.Parameters["@IdNew"].Direction = ParameterDirection.Output;

Direction InputOutput System.Data.ParameterDirection