说明：  C51语音播放源码 将语音按占空比放出。原语音为8位8KHz，则125us一个字节，现时钟主频近2MHz，周期为0.5us，这样一个字节占250个周期，而字节8位为256，可以近似为256个周期，实验应放在定时器中产生。 如果倍频，每个字节就可以产生两个波形，音质应更好
(C51 voice broadcast voice-source release by the duty cycle. The original voice for the 8-bit 8KHz, while 125us a byte, it is near the clock frequency 2MHz, cycle 0.5us, accounting for a 250-byte cycle, and 8 bytes for the 256, can be approximately 256 cycles, the experiment produced should be placed on timers. If the octave, each byte can have two waveforms, sound quality should be better)