Five Things to Consider When Choosing a VXI Controller

National Instruments, a leader in VXI control for more than 15 years, provides a complete VXI controller offering with a comprehensive software package for configuring, programming, and troubleshooting VXI/VME systems. From two-slot and single-slot embedded controllers to remote controllers using MXI-2, MXI-3, USB, 1394, and GPIB, National Instruments delivers controllers to meet your specific application needs. Consider the following five issues when choosing a VXI controller.

Company history and commitment to VXI

National Instruments is committed to making NI VXI customers successful by providing innovative products, world-class support, and the ability to maximize system longevity. As a consistent innovator in the VXI market, NI takes advantage of the latest PC processors and interfaces. Because getting the most out of investments is important to customers, National Instruments maximizes NI product life spans and offers ways to extend VXI system longevity through hybrid test systems.

Software

NI VXI software includes a broad range of tools from bus interface software to application development environments. When choosing a controller for a VXI system, make sure the bus interface software provides a comprehensive software package for configuring, programming, and troubleshooting VXI/VME systems to attain maximum system performance and development productivity. When evaluating the provided software, look for high-performance hardware drivers, flexible and intuitive high-level application programming interfaces (APIs), and a common configuration manager to reduce your time spent configuring the test system and developing tests.

In addition, select bus software that helps you create systems that are portable across a variety of controllers, such as embedded controllers or external computers that interface to VXI with MXI-2, MXI-3, USB 2.0, IEEE 1394, and IEEE 488 technologies. By doing this, you can maximize code reuse no matter what controller you use.

VXI controller features

When evaluating a VXI controller for a system, consider the various controller features. The following features impact system performance, the level of system control you have, and multiple mainframe synchronization.

VXI Addressing – NI controllers feature the MITE and MANTIS custom ASICs for accessing the VXI backplane resources. To access VXI memory or VXI devices, these controllers use the multiple MITE windowing scheme, so you can take advantage of all the VXI address space. The MITE exports independent VXI address windows, providing you with three completely user-configurable windows. You also can set each window size and location. This multiple windowing scheme alleviates the performance breakdowns created by constantly moving between the different address spaces.

DMA Transfers to and from VXI – With VXI controllers, you can perform block-mode transfers with one of the two on-chip DMA controllers on the MITE. Controlling external VXI devices often takes valuable CPU time, because the microprocessor typically shoulders the burden of transferring data to and from devices. However, MITE-based VXI controllers free up CPU processing time by moving the burden of block data transfers to one of the DMA controllers on the MITE. Instead of the computer microprocessor transferring the data and/or commands, NI-VXI/NI-VISA software uses the MITE ASIC to execute the block data transfers. While the MITE transfers the data, the processor can perform application-specific tasks, such as data presentation and analysis.

VXI Slot 0 Functionality – NI VXI controllers have full VXI Slot 0 capability, including a MODID register and a CLK10 source, as required by the VXIbus specification. You also can install the VXIpc-870B Series and VXIpc-770 Series embedded controllers in another slot and use them in the non-Slot 0 mode. No matter what your configuration needs, the VXIpc-870B Series and VXIpc-770 Series can automatically detect whether the controller is inserted into Slot 0 and automatically enable or disable the Slot 0 onboard circuitry without switches and jumpers.

VXI CLK10 Synchronization – NI VXI embedded controllers have an SMB connector on the front panel for an external clock. All of the NI VXI controllers can use this connector as an input for the 10 MHz VXI CLK10 signal. Most of the controllers also can use onboard programmable logic to configure the controller to drive its 10 MHz VXI CLK10 signal to this connector as an output. In this way, you can configure multiple mainframes to operate off a single 10 MHz system clock.

Advanced Trigger/Timing – With the VXI controllers, you have full software and hardware control of the VXI trigger lines. The controllers have two SMB trigger I/O connectors on the front panel for routing any TTL trigger line between the backplane and external devices. The controllers can respond to all VXI-defined protocols on all P2 TTL and ECL trigger lines at the same time. The hardware also includes an internal counter, which gives sophisticated event counting and interrupting on trigger edges and pulses, as well as generating pulse trains, variable length pulses, and pulse stretching.

VXI Interrupts – The VXI controllers can function as an interrupter and an interrupt handler for any or all of the VXIbus interrupt lines in a VXI mainframe. Using NI-VXI/NI-VISA software, you can program your application to notify you when any interrupt is
asserted and to assert any interrupt level with a programmable status. You can use the NI-VXI configuration software to assign which device handles each interrupt level.

The table outlines the controller features supported by each NI VXI controller.

Performance

In general, embedded VXI controllers offer maximum performance and the most compact size because they are installed directly into the VXI mainframe. The high-performance two-slot controllers offer faster processor speeds and more external ports, while the single-slot controllers help you maximize the slots you have in your chassis for modules.

Remote controllers provide the flexibility of controlling a VXI system from a remote PXI system, PC, or workstation. The MXI-2 and MXI-3-based controllers offer better overall performance while the USB 2.0, IEEE 1394 (FireWire), and GPIB interfaces provide lower-cost solutions. MXI-2 interface kits offer block-transfer performance comparable to embedded controllers with the additional flexibility and expandability of a desktop PC or workstation. With MXI-3 interface kits, the controlling computer can be up to 200 m away. The VXI-USB, a lower-cost remote controller, provides good word-serial performance and very good block-move performance. Because most computers come equipped with USB 2.0, the VXI-USB eliminates the need for a plug-in host controller card. A GPIB-VXI connection is well-suited for applications that are not data transfer-intensive and use primarily message-based instruments. The IEEE 1394 VXI interface kit boasts block performance faster than the GPIB-VXI/C. Determine the types of instruments in your system before selecting a VXI controller to match your system capabilities and requirements. The table shows a performance capability comparison for the various controllers.

Technical support

While NI VXI controllers are designed to be easy to use, it is important to get help when you need it. National Instruments offers direct product support. When you need an expert, you can contact one of hundreds of degreed applications engineers via phone or e-mail.

For 24-hour support, visit the award-winning NI technical support Web site or submit your question to the large NI VXI discussion forum user community. An active member probably has already tackled your problem or application challenge.

VXI Controllers

Feature	VXIpc-77x, VXIpc-870B	VXI/VME-PXI801x, VXI/VME-PCI801x, VXI-8350, VXI/VME-PCI802x, VXI/VME-PCI804x	VXI-USB
Interface and Cabling	Embedded	MXI-2	USB
VXIplug&play- Compliant	√	√	√
Slot-0 Compatibility	√	√	√
Direct Trigger and Interrupt Control	√	√	√
High- Performance DMA Transfers Using MITE Chipset	√	√	√
CLK10 Synchronization	Onboard External	Onboard External	Onboard External
Message- Based Communication	Optimized	Optimized	Optimized
Register-Based Communication	Optimized	Optimized	Supports
Small Word Serial	Best	Better	Good
Large Word Serial	Better (77x)/ Best (Rest)	Better	Good
Large Block Moves	Best	Best	Best
Small Block Moves	Better (77x)/ Best (Rest)	Best	Good
High-Level Access	Better (77x)/ Best (Rest)	Better	Good
Peeks	Better (77x)/ Best (Rest)	Better	Good
Pokes	Better (77X)/ Best (Rest)	Best	Good
Maximum Sustained Throughput	18.5 MB/s	14.5 MB/s	32 MB/s
Maximum Distance Support	0 m	20 m	5 m without extender
Operating System	Windows 2000/NT /XP VxWorks Linux	Windows 2000/NT /XP/Me /98 HP-UX, Linux, Solaris, Mac OS	Windows 2000/XP

VXI Controllers

Feature	GPIB-VXI/C	VXI-1394	VXI- PXI834x, VXI- PCI834x
Interface and Cabling	GPIB	IEEE 1394 (FireWire)	MXI-3, copper or fiber-optic
VXIplug&play- Compliant	√	√	√
Slot-0 Compatibility	√	√	√
Direct Trigger and Interrupt Control	√	√	√
High- Performance DMA Transfers Using MITE Chipset	−	√	√
CLK10 Synchronization	External	External	Onboard External
Message- Based Communication	Optimized	Optimized	Optimized
Register-Based Communication	Supports	Supports	Supports
Small Word Serial	Good	Good	Better
Large Word Serial	Good	Good	Better
Large Block Moves	Good	Good	Better
Small Block Moves	Good	Good	Better
High-Level Access	Good	Good	Better
Peeks	Good	Good	Better
Pokes	Good	Good	Best
Maximum Sustained Throughput	1 MB/s	12 MB/s	13 MB/s
Maximum Distance Support	4 m	4.5 m	200 m
Operating System	Windows XP/2000 /NT/Me /98 HP-UX, Linux, Solaris,  Mac OS, RTX	Windows 2000/NT /XP/ Me/98	Windows 2000/NT /XP/Me /98

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