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

VB与串行通信编程实例：单片机采用了51单片机，多机通信中采用了利SM2来区分是数据还是地址，效果还可以。其中RS485部分采用了隔离转换电路，采用高速光耦6N137-VB and serial communication programming examples: single-chip microcontroller with a 51, multi-machine communication using Lee SM2 to distinguish the data or address,