设施农业环境监控网络扩展

随着设施农业的发展，环境监控网络不断扩大，由于RS-485总线具有结构简单、使用方便、通信距离和数据传输速率适当及可靠性较高等特点在农业环境监控中得到广泛应用。但TIA、EIA-485规定一个连接最多可以有32个单位负载，为解决环境监控网络节点多于32个的问题，该文研究了基于单片机AT89C51的RS-485总线网络扩展方法，可以根据实际需要把RS－485总线扩展至4支路、8支路和12支路，该设计十分简单，成本也比较低，电路运行稳定可靠。

Bus network topology for environmental control of protected agriculture

With the development of protected agriculture, the size of environment control system is larger and larger. The RS-485 bus has the virtues of simpleness, convenience to use, appropriate distance of communication, proper rate of transmission and high reliability. It is widely used in the control of agricultural environment. But TIA EIA-485 stipulates that an RS-485 connection has no more than 32 noads. To solve the problem of more than 32 nodes in the communication network, a method of RS-485 bus topology based on single chip is put forward in the paper. The method adds the capacity of RS-485 bus. The bus network can extend to four, eight and twelve branches according to the concrete case. The design is simple and the cost is low. The circuit runs smoothly and reliably.