INT0的中断服务程序及脉宽测量

通过按键产生/INT0 有效信号，在P3.4 引脚上输出指示信号；并测量按键操作在/INT0引脚上产生的高电平的脉宽。注意：实际操作时，测试的脉冲宽度有可能超过16 位计数器的定时范围。操作时，考虑用蜂鸣器或指示灯作为状态提示。

-INT0 interrupt service routine and pulse width measurement

Produced by key/INT0 valid signal, the output signal indicating the P3.4 pin　and measure the pulse width of the key high-level operations on the/INT0 pin is generated. Note: the actual operation, the pulse width of the test is likely to exceed the range of 16-bit timer counter. Operation, considered as a status indicator buzzer or tips.