串口通訊，100 PB源碼，無控件，直接調用API，所以比控件穩定-Serial Communication, 100 PB-source, no control, directly call API, so the stability than the control

一个纯PB做的串口通信的例子，调用API，占用系统资源少。-PB to do a pure example of serial communication, call API, occupy less system resources.