Development of A USB-Based programmable SDLC measurement unit

USB-based portable measurement instrument has becoming more and more popular in field application. Recently, isolated RS-485 based synchronous data link control (SDLC) connection was used in aerospace payloads. Custom versions of SDLC protocol was designed for optimizations of specific applications, so do the SDLC protocol measurement units. A USB-based SDLC protocol measurement unit´s design is presented in this paper. The measurement system consists of a high speed USB connected measurement unit and a robust laptop computer. All the power the measurement unit need is supplied by the USB power cord. The SDLC protocol is implemented on FPGA, a high speed USB MCU is introduced to manage the high speed data link to the computer. We design a special structure to fit the requirement of flexible SDLC commands handling. An over-sampling serial data front end is introduced to support flexible data rate communication, test data shows that the measurement unit supports data rate within 2Mbps~10Mbps.