Considerations for implementing high performance VXI test systems

This paper is intended to inform the reader on some of the benefits as well as areas of concern that are present when performing new designs of VXI systems. This paper will first address topics dealing with the basic operational characteristics of VXI systems, then elaborate on system design issues dealing with throughput synchronization, multi-chassis implementations and connectivity to external devices. Hardware and software aspects of VXI design will also be covered. The software issues discussed will explore the application program interfaces (APIs) that are available for interfacing with VXI instruments and their evolution into the Virtual Instrument Software Architecture (VISA). Hardware issues covered will be directed at synchronization of VXI devices both internal and external to a chassis. Differences in implementation of asynchronous event handling schemes, as exemplified by the IRQ and event signals will be discussed. Other topics covered will deal in the operational differences between VXI instruments based on revision 1.3 specification versus the instruments based on the 1.4 version of the VXI specification. As an aid to understanding capabilities of VXI devices the low level differences between register based devices and message based devices when communicating over the VXI backplane will be discussed in detail. Discussion of when to use message-based devices and when to use register based devices will also be addressed. In an attempt to provide a system level understanding of VXI usage, the paper will also address topics such as interfacing to and from external devices