本文设计了基于USB2.0接口的RS485讯号仿真器。它通过终端应用程序软件设置串 列通信参数和数据帧发送格式，并在讯号仿真器内部形成讯号死循环反馈，即将实际发送的数据通过反馈回路回送给终端应用程序软件并显示出来。文中详细介绍了 USB接口芯片FT245R的工作原理及应用，并在MFC平台下调用FT245R的动态链接库接口函数进行终端应用程序软件设计。 -This paper is designed based on USB2.0 interface RS485 signal emulator. It is through the terminal application software to set serial communication parameters and send the data fr a me format, and the signal simulator developed within the loop feedback signal is about the actual data sent through the feedback loop back to the terminal application software and displayed. This paper details the USB interface chip FT245R the working principle and application platform in the MFC dynamic link library called FT245R interface function terminal application software design.