目前，在我国现场控制总线中，RS-485 使用最为普遍。RS－485 总线的共模输出电压在

-7V 至+12V 之间，具有抑制共模干扰的能力，数据传输速率最大为10Mbit/s，当波特率为1200bps 时最大的传输距离理论上可达15 千米。RS－485 网络所具有的设备简单、容易实现、传输距离远、维护方便等优点而被许多变频器厂家所采用。源码基于RS-485 变频器与PC 机串行通信的硬件特性，通信协议及软件实现，实验表明该通信软件稳定可靠，能直观的观看变频器的实际运行状态，并能比较方便的进行多组参数的设定和改写。通过此软件，极大的方便了工程师和客户对变频器的操控和掌握。本源码基于485串口通信的VB控制变频器，其控制电机的速度变化。-At present, in our country in the field control bus, RS- 485 using the most common. RS- 485 bus in the common-mode output voltage

7 v to+ 12 v, have the ability to inhibit common-mode interference, maximum 10 MBPS speed of data transmission, when the baud rate to 1200 BPS transmission distance theory can reach a maximum of 15 km. RS- 485 network of simple equipment, easy to implement, long transmission distance, convenient maintenance and been adopted by many inverter manufacturers. Source based on RS- 485 converter serial communication with a PC hardware features, communication protocol and software implementation, the experiment shows that the communication software is stable and reliable, can be intuitive to watch the actual running condition of frequency converter, and can be convenient for multiple sets of parameters setting and rewrite. Through this software, greatly convenient for engineers and customer manipulation and control of the inverter. The source based on 485 serial po