因RS-485接口具有良好的抗噪声干扰性，长的传输距离和多站能力等上述优点就使其成为首选的串行接口。因为RS485接口组成的半双工网络，一般只需二根连线，所以RS485接口均采用屏蔽双绞线传输。RS485接口连接器采用DB-9的9芯插头座，与智能终端RS485接口采用DB-9（孔），与键盘连接的键盘接口RS485采用DB-9（针）。(RS-485 interface has the advantages of good noise immunity, long transmission distance and multi station capability, which makes it the preferred serial interface. Because the RS485 interface consists of half duplex network, generally only two connections are needed, so the RS485 interface is shielded twisted pair transmission. RS485 interface connector adopts DB-9's 9 core plug socket, and the intelligent terminal RS485 interface adopts DB-9 (hole), keyboard interface with keyboard, RS485 adopts DB-9 (needle).)