CREDIT:
    begin
    if (coin_put_i)
        begin
        credit_accumulated <= credit_accumulated + coin_sum_bi;
        end
    else if (select_good_i)
        begin
        selected_good <= select_good_num_bi;
        check_credit <= credit_accumulated - select_good_cost_bi;
        if (check_credit < 0)
            begin
            state <= CHANGE;
            end
        else
            begin
            credit_accumulated <= check_credit;
            state <= DELIIVERY;
            end
        end
    else if (cancel_i)
        begin
        state <= CHANGE;
        end
    end