数据链路：两个或多个通信站之间的调制解调器、控制器或通信线路。
Data link: The communications lines, modems and controls between two or more data communications stations.
但是由于控制系统各异，通信协议不同，这些不同的RS485通信线路很难融合起来。
But it is difficult to blend these different RS485 lines because of different control systems and communication protocols.
前端设备：一种把一些通信线路与计算机系统联接起来的传输控制单元。
Front-end device: a transmission control unit that links a number of communication lines to a computer system.
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