Implementing digital interfaces with user programmable FPGAs

The electronics test engineer is constantly challenged by a myriad of digital interfaces. Military, Space, Communications, and Automotive electronics all utilize both industry standard and custom digital interfaces. Many of these interfaces are supported with test instrumentation that is dedicated to a specific interface or alternatively, a cycle-based, general purpose digital I/O instrument may be employed. Using dedicated test instrumentation can be very costly and general purpose digital I/O instrumentation can offer only a partial solution as well as requiring substantial programming / debugging, with either solution ultimately driving up the cost of test. A user-programmable FPGA-based solution can offer a cost-effective, alternative solution for supporting digital interfaces and specifically, serial interfaces. This paper will provide an overview of present day digital test interface requirements with a focus on serial digital interfaces which have become increasingly common for the control and monitoring of electronic modules and systems. These interfaces include both custom and industry standard versions such as SPI, I²C, RapidIO, Ethernet, or SpaceWire. For high speed serial interfaces, the use of SERDES (serial / deserializer) functionality in conjunction with interface-specific, functional logic can provide the basis for creating the required test instrumentation. The paper will discuss how user-programmable, FPGA-based instrumentation, when combined with commercially available IP (Intellectual Property) or custom logic cores, can provide cost-effective, flexible test instrumentation solutions which can potentially support multiple applications and a range of interfaces using a single, FPGA-based instrument.