用RS485通信，实现门禁系统的控制，本程序主要实现通信代码。用51单片机，MAX485芯片通信,Using RS485 communications, the implementation of Access Control Systems control, implementation of this procedure the main communications code. With 51 single-chip, MAX485 chip communication

基于RS485总线的51单片机主从通信方式的设计与实现 -51 based on the RS485 bus single-chip master-slave communication Design and Implementation