【摘要】 基于单片机RS-485总线网络扩展的总线转发器由AT89C51、通信芯片MAX491、上电复位芯片X25045及光电隔离芯片TLP521-4等组成。可为总线添加4个分支,外接128个节点。支路1控制字为56H,支路2为59H,支路3为65H,支路4为95H。打开分支前应关闭全部支路,P1口输出为55H。总线选择时约定命令控制字为0FEH。AT89C5通讯采用串口方式1,波特率8位可变。定时器为可自动装入参数的方式2,采用串口中断,波特率设置与上位机匹配。更多还原

【Abstract】 The bus transmitter of RS-485 bus extension based on microcomputer is mainly composed of AT89C51, MAX491, X25045 and TLP521-4. It can add 4 branches and 128 nodes. The control words of the four branches are respectively 56H, 59H, 65H, 95H. The port P1 should output 55H to turnoff all branches before opening any branch. When selecting bus, the control word is 0FEH. Mode one and changeable 8 bits baud rate are adopted during communication. The timer works at mode two at which parameter is loaded automatically. The AT89C51 is interrupted by serial port whose baud rate matches that of the host PC.更多还原