Glossary
Prefixes
| Symbol | Prefix | Value |
|---|---|---|
| p | pico | 10 -12 |
| n | nano | 10 -9 |
| µ | micro | 10 -6 |
| m | milli | 10 -3 |
| k | kilo | 10 3 |
| M | mega | 10 6 |
| G | giga | 10 9 |
| T | tera | 10 12 |
Numbers/Symbols
| nV | nanovolts | 10-9 volts |
| µV | microvolts | 10-6 volts |
| µΩ | microohms | 10-6 ohms |
| mΩ | milliohms | 10-3 ohms |
| MΩ | megaohms | 106 ohms |
| pA | picoamps | 10-12 amperes |
| nA | nanoamps | 10-9 amperes |
| µA | microamps | 10-6 amperes |
| mA | milliamps | 10-3 amperes |
A | |||
| A16/A24/A32 space | VXIbus address spaces. Address space is a set of 2n memory locations differentiated from other such sets in VXI/VMEbus systems by six signal lines known as address modifiers, where n is the number of address lines required to uniquely specify a byte location in a given space. Valid numbers for n are 16, 24, and 32.
A16 space is equivalent to the VME 64 KB short address space. In VXI, the upper 16 KB region is referred to as VXI configuration space. A24 space is equivalent to the VME 16 MB standard address space. A32 space is equivalent to the VME 4 GB extended address space. | ||
B | |||
| base address | A specified address that is combined with a relative address (or offset) to determine the absolute address of a data location. All VXI address windows have an associated base address for their assigned VXI address spaces. | ||
| bus master | A type of a plug-in board or controller with the ability to read and write devices on the computer bus. | ||
| byte | A grouping of adjacent binary digits operated on by the computer as a single unit. A byte consists of 8 bits. | ||
| byte order | How bytes are arranged within a word or how words are arranged within a longword. Motorola ordering stores the most significant byte (MSB) or word first, followed by the least significant byte (LSB) or word. Intel ordering stores the LSB or word first, followed by the MSB or word. | ||
C | |||
| Commander | A message-based device that is also a bus master and can control one or more Servants. A Commander can itself be a Servant to another Commander that is higher in the Commander/Servant hierarchy. | ||
| Commander/Servant hierarchy | The VXIbus specification defines a Commander/Servant communication protocol that you can use to construct hierarchical systems using conceptual layers of VXI devices. The resulting structure is like a tree. A Commander is any message-based device in the hierarchy with one or more associated lower-level devices, or Servants. A Servant is any device in the subtree of a Commander. A device can be both a Commander and a Servant in a multiple-level hierarchy.
A Commander has exclusive control of its immediate Servants' (one or more) communication and configuration registers. Any VXI module has one and only one Commander. Commanders use the Word Serial Protocol to communicate with Servants through the Servants' communication registers. Servants communicate with their Commander, responding to the Word Serial commands and queries from their Commander. Servants can also communicate asynchronous status events to their Commander through hardware interrupts, or by writing specific messages directly to their Commander's Signal register. | ||
| communication registers | In message-based devices, a set of registers that are accessible to the device's Commander and are used for performing Word Serial Protocol communications. VME devices and VXI register-based devices do not have communication registers. | ||
| configuration registers | A set of registers through which the system can identify a module device type, model, manufacturer, address space, and memory requirements. To support automatic system and memory configuration, the VXIbus specification requires that all VXIbus devices have a set of such registers. VME devices do not have configuration devices. | ||
| configuration space | The VXIbus specification reserves a section of VXI/VMEbus address space for automatic system configuration and base-level communication. This section is the upper 16 KB of what is known as the A16 address space, which is divided into 256 blocks of 64 bytes each for a maximum of 256 VXI devices in a single VXIbus chassis. Therefore, this section (known as VXIbus configuration space) begins at a base address of 0xC000 and ends at 0xFFFF. A unique 8-bit logical address identifies each device. The logical address determine which of these 256 blocks a VXI device resides at or uses. Each VXI device, therefore, has a unique location in the system.
You can calculate the offset, or starting address, of a device's 64-byte block of addresses using the following formula: offset = C000 hex + (Logical Address * 40 hex) or, in decimal: offset = 49152 + (Logical Address * 64) | ||
| controller (System Controller) | A controller is a device that can control other devices. A desktop computer with a MXI interface board, an embedded computer in a VXI chassis, a VXI-MXI, and a VME-MXI may all be controllers depending on the configuration of the VXI system.
A VMEbus System Controller is a device configured for installation in Slot 0 of a VXIbus chassis or Slot 1 of a VMEbus chassis. This device is unique in the VMEbus system in that it performs the VMEbus System Controller functions, including clock sourcing and arbitration for data transfers across the backplane. A MXIbus System Controller is a functional module that has arbiter, daisy-chain driver, and MXIbus cycle timeout responsibility. This device is always the first device in the MXIbus daisy-chain. | ||
D | |||
| device class | VXIbus devices are categorized by their supported protocols into the following four classes.
Message-based devices support both the VXIbus configuration and communication protocols. These devices have Commander and/or command-based Servant capabilities. Register-based devices have VXIbus configuration registers, but do not have communications registers. Typically, they have little or no local intelligence and can be controlled by message-based devices. Memory devices have VXIbus configuration registers that are used for either permanent or temporary data storage in blocks of RAM or ROM in VMEbus A24 or A32 address space. Extended devices have VXIbus configuration registers and a subclass register, which defines both standard and manufacturer-specific subclasses. The subclass further defines the functionality of an extended device, such as a chassis extender. The National Instruments VXI-MXI chassis extender is an example of an extended device. VME devices that do not implement the VXIbus configuration registers do not have a VXI device class. | ||
| DMA | Direct Memory Access; a method by which data is transferred between devices and internal memory without intervention of the central processing unit. Generally, DMA is the fastest and most efficient method for transferring data. | ||
| DRAM | Dynamic RAM (Random Access Memory); storage that the computer must refresh at frequent intervals. | ||
E | |||
| embedded controller | A computer plugged directly into the backplane of a PXI or VXI chassis. Some examples of embedded controllers are National Instruments PXI-8170 Series and VXIpc controllers. | ||
| extender | A device such as the VXI-MXI-2 or VME-MXI-2 that can map interrupt lines, trigger lines, or other signals into or out of a chassis. | ||
| external controller | A desktop computer or workstation connected to the VXI system via a MXI interface board. An example is a standard personal computer with a PCI-MXI-2 installed. | ||
F | |||
| fair requester | An MXIbus master that does not arbitrate for the MXIbus after releasing it until it detects the bus request signal inactive. This ensures that all requesting devices are granted use of the bus. | ||
G | |||
| GPIB | General Purpose Interface Bus; the industry-standard IEEE 488 bus. The GPIB is a cable bus that connects computers to test equipment. Hewlett-Packard developed the original GPIB in the late 1960s to connect and control their line of programmable instruments (at Hewlett-Packard, the GPIB is called the HP-IB).
In 1975, the Institute of Electrical and Electronic Engineers (IEEE) published ANSI/IEEE Standard 488, IEEE Standard Digital Interface for Programmable Instrumentation, which contained the electrical, mechanical, and functional specifications of an interfacing system. This bus is now used worldwide and is known by the following names:
The IEEE committee later added a supplemental standard, IEEE 488.2, Codes, Formats, Protocols, and Common Commands, which extended the IEEE 488 specification. IEEE 488.2 defines a bus communication protocol, a common set of data codes and formats, and a generic set of common device commands. It also defines a standard set of instrument commands in the Standard Command for Programmable Instrumentation (SCPI) document. GPIB became an industry standard for test and measurement systems. Because VXI was developed for this industry, many VXI devices use the IEEE 488.2 and SCPI commands. | ||
| GPIB-VXI/C debug mode | Loads the GPIB-VXI code instruments in a debug mode. Debugging a GPIB-VXI/C is described in detail in the GPIB-VXI/C User Manual. Normally, you should not place a GPIB-VXI/C into debug mode unless directed to do so by National Instruments technical support. | ||
H | |||
| HP/Agilent VISA | Refers to the Hewlett-Packard/Agilent implementation of the VISA specification. | ||
I | |||
| instrument driver | Instrument drivers are the tools for developing a system without programming the instruments themselves. By using instrument drivers, you do not need to learn any instrument command sets of data formatting routines. Instrument drivers contain high-level functions for specific instruments such as multimeters, scopes, and counters. Because the drivers have all the programming commands and data formatting routines for instruments, you can concentrate on developing systems rather than programming instruments. | ||
| interrupt | A means for a device to notify another device that an event occurred. This asynchronous event suspends normal activity and temporarily diverts activity to an interrupt handling function. | ||
| interrupt handler | A functional module that detects interrupt requests generated by interrupters and performs appropriate actions. | ||
L | |||
| LabVIEW | LabVIEW is a graphical programming system designed for easy construction of sophisticated, user-defined instrumentation systems. It has the flexibility necessary to harness the high performance of VXI, along with a programming methodology that dramatically reduces application development time. LabVIEW is fully VXIplug&play compliant to give you the full benefits of VXIplug&play technology. | ||
| LabWindows/CVI | LabWindows/CVI is an integrated software system for rapid development, prototyping, and operation of test and measurement and data acquisition applications. It provides a full-function C programming environment for the Windows and Sun Solaris platforms. LabWindows/CVI applications are written in industry-standard program code, and are flexible, modular, extensible, and portable between either platform. National Instruments offers VXI/VME development systems for these two platforms that link the NI-VXI driver software into LabWindows/CVI to control VXI instruments from either embedded VXI/VME controllers or external computers equipped with a MXI interface. LabWindows/CVI is fully VXIplug&play compliant to give you the full benefits of VXIplug&play technology. | ||
| logical address | An 8-bit number that uniquely identifies the location of each VXIbus device's configuration registers in a system and indicates Commander and Servant relationships. The A16 register address of a device is C000h + Logical Address * 40h. | ||
| Logical Address 0 | If a local device, such as the external controller, is configured at Logical Address 0, it is responsible for the following VXI Resource Manager operations at startup, as defined by the VXIbus specification:
The Startup Resource Manager also has the following capabilities, which extend beyond the requirements of the VXIbus specification:
| ||
| longword | Data type of 32-bit integers. In Longword Serial Protocol, Commanders and Servants communicate with 32-bit data transfers instead of 16-bit transfers as in the standard Word Serial Protocol. | ||
M | |||
| message-based communication | Message-based devices implement the defined VXIbus registers and communication protocols. These devices are able to use Word Serial Protocol to communicate with one another through communication registers, which are optional registers that register-based devices do not use. Message-based devices communicate at a very high level using ASCII characters, just like GPIB. The ASCII characters that you send to a message-based device must be in the device's specific language, but you do not need to be concerned with module-specific registers (that is, binary reading and writing). Many VXI message-based instruments are also SCPI-compatible. | ||
| MXI/MXI-2 | The Multisystem eXtension Interface bus (MXIbus) is a multidrop parallel bus architecture designed for high-speed communication between devices. The MXIbus is a general-purpose gateway that you can use to communicate between two or more devices, such as personal computers, workstation computers, VXIbus chassis, VMEbus-based computers, stand-alone instruments, or modular instruments.
MXI-2 is the second generation of the National Instruments MXIbus product line. MXI-2 expands the number of signals on a standard MXIbus cable by including VXI triggers, all VXI interrupts, CLK10, SYSFAIL*, SYSRESET*, and ACFAIL*. | ||
N | |||
| NI Spy | The National Instruments utility that tracks an application's calls to NI-VISA, the NI-VXI API, and NI-488.2. You can use this logging utility to obtain a list of the functions the applications calls and quickly find which ones did not execute properly. | ||
| NI-VISA | NI-VISA is the native API for communicating with VXI/VME devices. NI-VISA is the National Instruments implementation of the VISA I/O standard, which is a common interface to many types of instruments (such as VXI, GPIB, PXI, serial, TCP/IP, etc.). NI-VXI is optimized for use through NI-VISA, and National Instruments recommends using NI-VISA to develop all new VXI/VME applications. | ||
| NI-VXI | NI-VXI is the software package that ships with National Instruments VXI controllers. NI-VXI includes Measurement & Automation Explorer (MAX), NI-VISA, NI Spy, Resource Manager (Resman), VXI device drivers, and other utilities for configuring and controlling your VXI system. | ||
| NI-VXI API | The NI-VXI API is an optional development environment that is not part of the default NI-VXI installation. The NI-VXI API was developed before NI-VISA; while NI-VXI still supports the NI-VXI API, National Instruments recommends using NI-VISA for all new VXI/VME applications. If you must develop an application using the older NI-VXI API, run the NI-VXI installer and select the appropriate option in the custom installation screen. | ||
| non-Slot 0 | Any slot in a VXI chassis except for the first slot.
| ||
| nonprivileged access | One of the defined types of VMEbus data transfers; indicated by certain address modifier codes. Each defined VMEbus address space has a defined nonprivileged access mode. | ||
P | |||
| peek | To read a single byte, word, or longword from a particular address. This can be accessed either through a direct dereference of a pointer or through the NI-VISA function viPeekX or NI-VXI API function VXIpeek. | ||
| pointer | A data structure that contains an address or other indication of storage location. | ||
| poke | To write a single byte, word, or longword to a particular address. This can be accessed either through a direct dereference of a pointer or through the NI-VISA function viPokeX or NI-VXI API function VXIpoke. | ||
| pseudo logical address | A number signifying an address that you can use to integrate VME devices with VXI devices. Because the Resource Manager does not configure VME devices, you must manually add the devices. You can choose a number in the range of 256 to 511 (255 and below are reserved for VXI devices). Enter other appropriate information into the various fields of the editor, and when you run Resource Manager, it can then properly configure the various device-specific VME address spaces and VME interrupt lines. | ||
R | |||
| register-based communication | A register-based device is a Servant-only device that supports VXIbus configuration registers. These devices do not implement the optional communication registers that are required for message-based communication. Register-based devices are typically controlled by message-based devices via device-dependent register reads and writes. The obvious advantage of this is speed; register-based devices communicate literally at the level of direct hardware manipulation. There is no command string parsing overhead. The disadvantage is that each device is different and requires customized manipulation of registers. Thus, the instrument interface is not portable across instruments. | ||
| Resource Manager (Resman) | A message-based Commander, located at Logical Address 0, that provides configuration management services such as address map configuration, Commander and Servant hierarchy mappings, and self-test and diagnostic management. On system startup, the VXI System Controller executes the Resource Manager to automatically configure the entire system. This automatic startup configuration eases system integration. After the Resource Manager has executed, the system is ready to go. You can also execute the Resource Manager interactively at any time if you are reconfiguring system resources. | ||
S | |||
| Servant | A device controlled by a Commander in the Commander/Servant Hierarchy. A Servant can itself be a Commander to Servant devices that are lower in the hierarchy. | ||
| shared memory | A block of memory that is accessible to both a client and a server. The memory block operates as a message buffer for communications. | ||
| Slot 0 | The first slot in a VXI chassis. A device configured for installation in this slot is unique in the VXI system in that it performs the VMEbus System Controller functions, including clock sourcing and arbitration for data transfers across the backplane.
| ||
| soft front panel (SFP) | See VXIplug&play soft front panel. | ||
| status/ID | A value returned during an IACK cycle. In VME, usually an 8-bit value which is either a status/data value or a vector/ID value used by the processor to determine the source. In VXI, a 16-bit value used as a data; the lower 8 bits form the VXI logical address of the interrupting device and the upper 8 bits specify the reason for interrupting. | ||
| supervisory access | One of the defined types of VMEbus data transfers; indicated by certain address modifier codes. | ||
| SYNC protocol | The most basic trigger protocol, simply a pulse of a minimum duration on any one of the trigger lines.
You can assert a pulse for a minimum of 30 ns, followed by a minimum nonassertion period of 50 ns. There is no acknowledgment from the receiver(s). Any module can issue the triggering pulse, but the module cannot be sure that the pulse has been received. | ||
| system registry | The system registry is used to store persistent information by both the operating system and many programs. See your operating system documentation for more information. | ||
T | |||
| trigger | Either TTL or ECL lines used for intermodule communication. | ||
U | |||
| user window | A region of PCI address space reserved by the external controller or VXIpc series embedded controller for use via low-level function calls. The MapVXIAddress() and viMapAddress() functions use this address space to allocate regions for use by the VXIpeek()/VXIpoke() and viPeekXX()/viPokeXX() functions. | ||
V | |||
| VIC/VICtext | VXI Interactive Control program, a part of the NI-VXI API bus interface software. Used to program VXI devices, and develop and debug VXI application programs. It is also very useful for developing an understanding of how you can use the NI-VXI API to interact with your VXI devices. Called VICtext when used on text-based platforms.
| ||
| VISA | VISA is a multivendor I/O software standard approved by the VXIplug&play Systems Alliance. It provides a common foundation for the development, delivery, and interoperability of high-level multivendor system software components, such as instrument drivers, soft front panels, and application software.
NI-VISA is the National Instruments VISA solution. | ||
| VISAIC | VISA Interactive Control (VISAIC) utility, a part of the NI-VISA interface software. You can use this utility to interact with devices using NI-VISA. This is very useful for developing and debugging VISA application programs. It is also very useful for developing an understanding of how you can use VISA to interact with your devices. | ||
| VME | Versa Module Eurocard or IEEE 1014. | ||
| VME64 protocol | Devices that support VME64 protocol can transfer data in 64-bit increments to double traditional VXI throughput to 80 Mbytes/s. | ||
| VXI | VMEbus Extensions for Instrumentation. Introduced by the VXIbus Consortium in 1987, the VXIbus (IEEE 1155) standard combines the best technology from GPIB instruments with modern computer bus architecture—VERSAbus Module Eurocard (VME). VXI uses a chassis with modular instruments on plug-in boards. Due to its VMEbus background, VXI features higher performance and more precise timing and synchronization between instruments. It is also smaller than GPIB rack-and-stack instruments. Yet unlike VME, VXI defines a standard communication protocol to certain devices. Through this interface, you can use common ASCII commands to control the instruments, just as with GPIB. The VXIbus specification is an extension of the VMEbus (IEEE 1014) specification. As an electromechanical superset of the VMEbus, the VXIbus uses the same backplane connectors as VME, the same board sizes, and the same signals defined in the VMEbus specification. The VXIbus adds two board sizes, changes module width, and defines additional signals on the backplane. | ||
| VXI embedded controller | A computer plugged directly into the backplane of a VXI chassis. An example is the National Instruments VXIpc series. | ||
| VXI signal | Any communication between message-based devices consisting of a write to a Signal register. Sending a signal requires that the sending device have VMEbus master capability. | ||
| VXI trigger | VXI triggers are a backplane feature that VXI added to the VME standard to achieve the required timing and signaling propagation between controllers and/or instruments. Every VXI board with a P2 connector has access to eight 10 MHz TTL trigger lines; if it has a P3 connector, it also has access to six 100 MHz ECL trigger lines. The VXIbus specification defines several trigger protocols that your application can use for device synchronization, for stepping through tests, or for a command path. The most basic protocols are SYNC, ASYNC, SEMI-SYNC, START/STOP, and ON/OFF. | ||
| VXIplug&play soft front panel | VXIplug&play-compliant instruments have software that can run without a programming environment and can produce a soft front panel (SFP). The SFP is a test application that represents and controls the instrument functions in an interactive way. They use a graphical interface and a mouse pointing device to manipulate simulated knobs, buttons, controls, and displays. You can use the SFP to check the operation of the instrument, verify and correct configuration and installation, and interact with the instrument. | ||
W | |||
| window | All accesses to the VXI/VMEbus address spaces are performed by reads and writes to particular offsets within the local CPU address space, which are made to correspond to addresses on the VXI/VMEbus (using a hardware interface). Windows are the areas where the address space of the local CPU is mapped onto the VXI/VMEbus. The sizes and numbers of windows present vary depending on the hardware being used. | ||
| word | The standard number of bits that a processor or memory manipulates at one time. Microprocessors typically use 8-, 16-, or 32-bit words. Standard Word Serial Protocol defines a word as 16 bits. | ||
| word serial protocol | The simplest required communication protocol supported by message-based devices in the VXIbus system. It uses the A16 communication registers to perform 16-bit data transfers using a simple polling handshake method. All message-based devices are required to support this protocol. Word Serial Protocol transfers data messages to and from devices serially, one byte (or word) at a time through the device's communication registers. | ||
