如何从串口获取最近读取的记录？

Question

我是vb.net的新手，我正在尝试开发衡器应用程序。我一直停留在串行端口一次读取多次的阶段，但我只想从串行端口获取最后读取的值港口。请参考以下代码和屏幕截图。提前致谢。我使用了以下代码：

$('.qty_input').keyup(function () {

    var qtyValue = $('.qty_input').val();
    // these 4 statements are executed no matter what. 
    // there is no point in duplicating them in each if-then block
    for(var i=1; i<=4; i++) {
        if ($('option[value="'+i+'"]').parent("span").length) {
           $('option[value="'+i+'"]').unwrap('<span/>');
        }
    }


         // the pattern for the next part is simple
         // execute 4 statements of jQuery but exclude one part per each if-then block
         if (qtyValue >= number1 && qtyValue <= number10) { exclude(1); }
    else if (qtyValue >= number2 && qtyValue <= number20) { exclude(2); }     
    else if (qtyValue >= number3 && qtyValue <= number30) { exclude(3); }        
    else if (qtyValue >= number4 && qtyValue <= 999999)   { exclude(4); }        

    function exclude(num) {
        // loop from 1 to 4 to execute the same for each part
        // but only exclude the one statement that is passed 
        // into the function
        for(var i=1; i<=4; i++) {
            if(i!=num) {
                if (!$('option[value="'+i+'"]').parent("span").length) {
                     $('option[value="'+i+'"]').wrap('<span/>')
                }
            }
        }
    }
});

Here is screenshot of output I am getting