此超声波测距程序用汇编代码编写，测量精度高，12M晶振可达1mm，稍微修改亦可成为高精度脉宽测量程序，带有仿真图。-The ultrasonic ranging program written in assembly code, high precision, 12M crystal up to 1mm, a slight modification can be a high-precision pulse-width measurement procedures, with a simulat