1、 8051内部定时计数器T0，按计数器模式和方式1工作，对P3.4（T0）引脚进行计数。将其数值按二进制数在P1口驱动LED灯上显示出来。

2、外部事件计数脉冲由P3.4引入定时器T0。单片机在每个机器周期采样一次输入波形，因此单片机至少需要两个机器周期才能检测到一次跳变。这就要求被采样电平至少维持一个完整的机器周期，以保证电平在变化之前即被采样。同时这就决定了输入波形的频率不能超过机器周期频率。-Internal timing counter T0 1, 8051, according to counter mode and methods of 1, to P3.4 (T0) pin count. Its value according to the binary number displayed on the P1 mouth drive leds.

2, external event count pulse introduced by P3.4 T0 timer. SCM in each machine cycle sampling the input waveform, so SCM needs at least two machine cycles to detect a jump. This request is sampling level to maintain at least one full machine cycle, in order to make sure the level before they can change by sampling. At the same time it determines the frequency of the input waveform frequency cannot exceed the machine cycle.