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Question What is Register Based I/O? Solution In general with respect to VXI based hardware, there are two industry wide standards for communicating to hardware. Message based and register based input and output. Instruments can utilize one or both protocols. Register based I/O is communication to hardware using direct register access to perform writes and reads. The SMIP platform is VTI Instrument’s family of VXI based switching products which uses register based I/O to control the state of switches. In the simplest terms, users can write direct to registers in the VXI address space to control large groups of relays with one transaction. For example, writing or reading to a 16 bit register accomplishes commanding or querying the state of 16 individual relays with one hardware communication. In general, the advantage of register based I/O is reduced test times due to significant reductions in communication transactions. Specifically, significant amounts of functionality can be executed with single hardware transactions. However, this increased efficiency introduces burden on the user in terms of software development and the time it takes to thoroughly understand a particular instrument’s register structure and operation. More specifically, the user interface is presented at a lower level requiring some up front SW development to create a more intuitive user interface. VISA is used industry wide as the standard software interface for sending both register based and message based commands to VXI instrumentation.