private void cmdGetProductCode_Click(object sender, EventArgs e)
        {
            string  vProductCode = "";
            Boolean vRet;
            int     vErrorCode = 0;

            txtProductCode.Text = "";
            lblMessage.Text     = "Waiting...";
            Application.DoEvents();

            vRet = bpc.EnableDevice(Program.gMachineNumber, 0); // 0 : false
            if (!vRet)
            {
                lblMessage.Text = util.gstrNoDevice;
                return;
            }

            vRet = bpc.GetProductCode(Program.gMachineNumber, ref vProductCode);
            if (vRet)
            {
                txtProductCode.Text = vProductCode;
                lblMessage.Text     = "Success";
            }
            else
            {
                bpc.GetLastError(ref vErrorCode);
                lblMessage.Text = util.ErrorPrint(vErrorCode);
            }

            bpc.EnableDevice(Program.gMachineNumber, 1); // 1 : true
        }