With modular instrumentation, developers can take advantage of open, multivendor standards and software flexibility to create a user-defined solution for their specific application needs. By using a modular architecture and open standards, they can easily integrate components from multiple vendors into one system and scale the system as needed. With high throughput, low latency, and software flexibility, developers can create a user-defined test system that is able to meet many application performance needs. Modular instrumentation buses deliver better throughput and latency in comparison to stand-alone instrumentation buses, which helps with many application needs like high-speed data streaming. By taking advantage of an open software model and PC processing power, users can extract all the measurements they require from the data provided by modular instruments. This gives users the flexibility to design a system as needed and pay only for the components required for the application.
VXI – The VXI Consortium was formed in 1987 with a charter that defined a multivendor instrument-on-a-card standard. Since that time, the consortium has defined system-level components required for hardware interoperability. The IEEE officially adopted the VXI specification, IEEE 1155, in March 1993. The VXIplug&play Systems Alliance, founded in September 1993, sought a higher level of system standardization to cover all VXI system components. By focusing on software standardization, the alliance defined standards to make VXI systems easy to integrate and use while maintaining multivendor software interoperability. With the success of multivendor standards and solid technical specifications, VXI is backed by more than 250 vendors, with more than 1000 products available. The success of VXI as an open, multivendor platform is a testament to the value of multivendor standards.
VXI is used in many different applications ranging from test and measurement and ATE to data acquisition and analysis in both research and industrial automation. Although some VXI systems today are purely VXI, many users are migrating to VXI by integrating it into existing systems consisting of GPIB instruments, VME cards, or plug-in data acquisition boards. Users can control a VXI system with a remote general-purpose computer using the high-speed Multisystem eXtension Interface (MXI) bus interface or GPIB. They can also embed computers into VXI chassis and control the system directly. Whatever a user’s system configuration needs may be, VXI offers the flexibility and performance to take on today’s most challenging applications.
PCI and PXI – Introduced in the early 1990s, PCI was first implemented as a chip-to-chip interconnect to replace the fragmented ISA bus. The PCI bus offered several advantages over previous bus implementations including processor independence, buffered isolation, bus mastering, and true plug-and-play operation. Typically not used directly for instrument control, the PCI bus serves as a peripheral bus to connect GPIB or serial devices for instrument control. Also, due to its high bandwidth, PCI is used as a carrier bus for modular instruments where the I/O bus is built into the measurement device.
PXI combines PCI electrical-bus features with the rugged, modular, Eurocard mechanical packaging of CompactPCI and adds specialized synchronization buses and key software features. This makes it both a high-performance and low-cost deployment platform for test, measurement, and control systems. These systems serve applications such as manufacturing test, military and aerospace, machine monitoring, automotive, and industrial test. With PCI-based communication, PXI benefits from low latency and high throughput at 132 MB/s. In addition, PXI provides additional timing and triggering with a 10 MHz reference clock, an eight-line trigger bus, and STAR trigger lines that feature dedicated trigger lines with intermodule skew within 1 ns. PXI is heavily used as a platform for modular instrumentation, offering an attractive alternative to traditional stand-alone instrumentation through compact, high-performance measurement hardware devices with integrated timing and synchronization resources.
PCI Express – As PC applications become more bandwidth-intensive, the PCI bus is reaching its physical limits in many situations. As a result, the PCI-SIG, the standards body that defines PCI, has introduced PCI Express, with the main goals of providing a scalable, low-cost interface that serves many different markets and delivering compatibility at the software level with existing PCI card drivers and software. Compatibility with the PCI addressing model is maintained to ensure that all existing applications and drivers operate unchanged. An evolution of PCI, PCI Express provides a basic communication lane of 250 MB/s in each direction in a x1 implementation and up to 4 GB/s in a x16 implementation. In addition, by connecting each PCI Express slot to a switch fabric, PCI Express offers independent bandwidth to each slot as opposed to the shared bandwidth in PCI. Designed with compatibility needs in mind, PCI Express uses a well-designed layered architecture to ensure compatibility with future generations as well as software compatibility with PCI. As with PCI, PCI Express is typically not used directly for instrument control but as a peripheral bus to connect GPIB devices to PCs for instrument control. Because of its tremendous speed, PCI Express can be used as a carrier bus for modular instruments.
PXI Express – As its use of PCI in the communication backplane helped drive the rapid adoption of PXI, PXI Express has the ability to meet even more application needs by integrating PCI Express into the PXI standard. By taking advantage of PCI Express technology, PXI Express increases the available PXI bandwidth from 132 MB/s to 6 GB/s for a more than 45 times improvement in bandwidth while maintaining software and hardware compatibility with PXI modules. With this enhanced performance, PXI can reach into many new application areas, many of which were previously served only by expensive and proprietary hardware. With the software compatibility of PCI Express, the standard software framework provided by PXI will carry into PXI Express. To provide hardware compatibility, the new CompactPCI Express specification defines a new hybrid slot that gives engineers the ability to install modules with either a PCI or PCI Express architecture in a slot. With this technology, engineers and vendors can preserve their existing investments in PXI systems and products through both hardware and software compatibility.