说明：  在方式2计数期间，OUT端为高，当减到0，OUT端输出低脉冲。本实验用此低脉冲触发微控制器的中断。方式3是方波发生器方式，计数值N为偶数时，输出为对称方波，前N/2期间，OUT输出为高，后N/2期间，OUT为低。本实验中，时钟CLK信号由ALE接入，设Q0为输出频率，Q1为ALE频率，则：计算初值=Q1/Q0.
(During the counting mode 2, OUT terminal is high, when reduced to 0, OUT-ended output low pulse. In this study, low pulse triggered by the microcontroller interrupt. Mode 3 is a square wave generator mode, the count value N is even, symmetrical square wave output, the first N/2 periods, OUT output is high, then N/2 periods, OUT is low. In this experiment, the clock CLK signal from the ALE access, set the output frequency of Q0, Q1 for the ALE frequency, then: Calculate the initial value = Q1/Q0.)