广州周立功单片机发展有限公司Tel：(020)3873097738730977Fax：38730925http://www.zlgmcu.comi目录第1章RS-485选型及应用指南.........................................................................11.1RS-232/422/485标准...............................................................................................11.1.1RS-232标准.....................................................................................................21.1.2RS-422/485标准..............................................................................................21.2RS-485/RS-422芯片................................................................................................51.2.1增强型低功耗半双工RS-485收发器－SP481E/SP485E..............................71.2.21/10单位负载RS-485收发器－SP481R/SP485R.....................................101.2.3+3.3V低功耗半双工RS-485收发器－SP3481/SP3485..............................131.2.4增强型低功耗全双工RS-422收发器－SP490E/SP491E............................151.2.5+3.3V低功耗全双工RS-422收发器－SP3490/SP3491..............................201.3RS-485接口电路...................................................................................................221.3.1基本RS-485电路...........................................................................................221.3.2隔离RS-485电路...........................................................................................231.3.3上电抑制电路.................................................................................................241.3.4RS-485自动换向电路....................................................................................241.4RS-485通讯协议...................................................................................................251.4.1ModBus协议(RTU模式)...............................................................................251.4.2多功能电能表通讯规约(DL/T645-1997)......................................................271.5RS-485程序设计...................................
