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介绍了用单片机实现四相相对调制的一种方法。该方法采用查表法，即事先将可能出现的波形样点值经计算后，按一定的规律存放在存贮器中。单片机收到不同的码组后，经过运算找出波形的首地址，再依次输出各个样值到Ｄ／Ａ转换器。详细介绍了各种波形样值的计算方法，给出四相相对调相首址的计算公式，并列出了Ｂ类方式前后码元间相位、首址对照表。对升余弦包络调制也做了较细的分析。给出了８种波形、每种波形取１２个样值的十六进制编码表。画出了主程序和四相相对调制子程序流程图以及硬件电路框图。在数码率不太高的情况下采用单片机实现四相相对调制较容易，硬件电路较简单。
A method of realizing relative modulation of four phases by single chip is introduced. The method uses the look-up table method, that is, the waveform samples that may appear in advance are calculated and then stored in the memory according to a certain rule. After the microcontroller receives the different code groups, the first address of the waveform is found through the operation, and then the various samples are output to the D / A converter in turn. The calculation method of various waveform samples is introduced in detail. The formula of four phase relative phase modulation phase address is given, and the phase and the first address comparison table of symbols before and after class B is listed. The raised cosine envelope modulation is also analyzed in detail. Eight waveforms are given, each of which takes a sample of twelve hexadecimal code tables. Draw the main program and four phase relative modulation subroutine flow chart and hardware circuit diagram. In the case of digital rate is not too high, the use of single-chip relative to the four-phase modulation easier, the hardware circuit is simpler.