The modulation of the modem is implemented by polling software look - up table , which has the merits of coding easily , less data calculation and fast operation , etc . the modem also has the ability of restoration and the communication software in data terminal has strong function of controlling 该调制解调器具有很强的自愈功能，数据终端的通信软件对调制解调器具有较强地控制能力，因而能适应复杂的工作环境，能迅速摆脱干扰的影响，恢复正常地通信联络。
The article analyzes the development schemes of the host computer interface card , the adapter principle of the printer and reasons of selecting it . having studied signals of printer ports further , thus i determined the communication mode between the host computer and the slave computer , and designed communication circuit . the question of programming has been discussed 论文分析了上位机计算机接口卡的开发方案，并行打印机接口原理和选用它的原因，研究了打印机端口信号，决定了通信联络方式，设计出上位机通讯硬件电路，并研究了上位机编程问题。
