一种实现无极性RS-485通信的探讨

Research of Non-polar RS-485 Communication

RS-485是一个定义平衡数字多点系统中的驱动器和接收器的电气特性的标准,该标准由电信行业协会和电子工业联盟定义,使用该标准的数字通信网络能在远距离条件下以及电子噪声大的环境下有效传输信号。RS-485有两线制和四线制两种接线,四线制只能实现点对点的通信方式,现很少采用,现在多采用的是带有极性的两线制接线方式。但随着中国国家电网智能电表改造项目的推进,在以亿计的电表使用带极性的两线制RS-485接入后,难免出现一定比例的接错现象,基于此许多厂家也设计出了无极性的RS-485芯片。然而无极性RS-485的稳定性和抗干扰却不如有极性的RS-485强,因此如何既能保证通信的可靠性又能实现无极性RS-485通信成为一个极具实用性的课题。

RS-485 is a standard of transceivers electrical characteristics in balanced and multipoint digital systems, which is set by the Electronics Industry Alliance（EIA） and Telecommunications Industry Association（TIA）.Digital communications networks implementing the standard can be used effectively over long distance and in electrically noisy environments. Compared to 2-Wire system, 4-Wire system is seldom used for its limitation in point-topoint transmission. Therefore 2-Wire system is mostly adopted in polar RS485. However with the application of 2-wire polar RS-485 in billions of smart meters, the polar of port A or B is inevitably mixed. Aiming at the problem, non-polar RS-485 chip is published. As the stability and interference immunity of non-polar RS-485 cannot be compared with polar RS-485, how to ensure the stability of non-polar RS-485 communication is a useful issue.