Electronic Design

Accelerated Design Verification And VXI Make A Perfect Match

Need To Account For Unexpected Operating Environments? The VXIbus Is The Way To Go For Hardware-In-The-Loop Testing Techniques.

To paraphrase a famous quote, electronic devices, and embedded systems in particular, sometimes boldly go where no other device has gone before. Simply put, the devices find themselves in a multitude of unexpected operating environments—some of which may not have been intended by the design engineer.

How, then, do design teams verify a new device's operation over the breadth of situations it may encounter? To answer this question, it's beneficial to understand the interdependence between the fault spectrum and the use model. One potential technique, adapted from software design, is hardware-in- the-loop, or accelerated-design-verification, testing. Thanks to recent advances in computational and measurement technology, the VXIbus (VME eXtensions for Instrumentation bus) lends itself to hardware-in-the- loop testing as a means to gain sufficient information regarding the fault spectrum in a dynamic environment.

Figure 1 shows a map of the size of the fault spectrum as it relates to the complexity of an operational environment for an electronic device. In this case, as the operational environment becomes more complex, the fault spectrum increases. An example might be the use of a personal computer in the confines of a home, versus one used as an operational component onboard a jet aircraft. The noise, shock, and cooling issues of the jet may precipitate more faults than the PC used in the home. This is depicted here as a larger circle when the temperature increases. This assumes, of course, a benign home environment rather than one where a two-year-old places a peanut butter sandwich in the fan on the back of the PC.

An excellent example of accelerated testing is illustrated in the automotive industry. Every July, auto racers from around the world arrive in Colorado Springs, Colo., to face the challenges of a race whose venue is the beautiful, but rugged, terrain of the Rocky Mountains. The challenge for both car and driver is the Race to the Clouds, a grueling hill climb to the summit of 14,110-ft Pike's Peak. The course is a twisting and winding gravel road called the Pike's Peak Highway. In just over 12 mi., drivers will experience a 10,000-ft change in elevation, and must manage their cars through 156 hairpin turns.

Casual observers might wonder about the race team's concern for the design of their car's electronic control module (ECM). Each second, this module relates the oxygen sensor input to the torque, and mixture of gas and air as the altitude increases. An engine that starts to lose power as the finish line approaches reflects poorly on the module and its designers.

A highly complex and dynamic environment such as this precipitates incipient failures in engine control modules. After talking with a number of ECM designers, we made a proposal regarding a design-verification scheme that provided greater fault coverage. The idea was to subject the ECM to electronic emulation of the race's environmental conditions. The system would emulate the signals for the ECM with very-large changes in altitude, temperature, pressure, and throttle, along with dynamic changes in the revolutions per minute. This accelerated test process would precipitate incipient failures. The goal was to test design alternatives before moving to manufacturing.

One other example points out that this style of verification can cross industry segments. Designers of telecom amplifiers have reached quality production rates with faults in the parts-per-million (PPM) range. It began when members of an engineering team were confronted by an experienced technician who had the reputation of "knowing" which amplifiers would fail first. Much to the designers' amazement, the track record for this technician was indisputable. After much cajoling, the technician let the engineers in on the secret. The technician would put the amplifiers into operation, then loosen the connectors and monitor which amplifiers provided the best output.

In this case, the technician would make a measurement of the outgoing signal on an oscilloscope with a degraded signal on the input. If the amp gave an output that was sustained within the grease marks on the scope, the technician was fairly certain the amplifier would stand up better than the other amplifiers.

This gave the designers an idea about how to improve the quality of the amplifiers. They used the more-difficult, degraded-signal test as part of their design verification when selecting alternate amplifier designs to pass on to manufacturing. By doing so, the designers were able to precipitate failure modes early in the design process, and not in the field.

In an eye diagram, for example, amplifiers within the light-green area yield better longevity (Fig. 2). This saves time, money, and resources. Now, instead of failure rates measured in the 1% range, designers were boasting of failures in the parts-per-million range.

The idea of accelerated testing is not just focused on temperature or the signals found in a mechatronic device. Another example is accelerating the crystal frequency of an oscillator to higher and lower frequencies. The idea is to uncover hidden faults by pushing and pulling the system into a metastable state. This may mean changing the clock frequency in a dynamic way, rather than with simple static steps. That is, the designer might consider increasing and decreasing the frequency as if it were modulated by 60, 120, or 400 Hz. Designers could vary the power to the board by oscillating the supply voltages, or injecting larger surges as might be found on a "poor-quality" power line.

The idea is not just to look for catastrophic failures, but to measure irregularities, or look for changes in a waveform signature as a device operates in this mode. The technique is somewhat analogous to identifying modes of resonance in a mechanical system. In this case, however, the impetus for failure is an electrical impulse.

The goal is to develop a map of the fault spectrum as it relates to changes in the environment. To reach this goal, designers need an electronic stimulus and measurement architecture that lends itself to accelerated testing. It must be one that adapts to complex environmental models with very-fast system throughput.

The VXIbus architects, made up of a consortium of vendors, forged a unique standard that provides fast measurement speed and high data throughput in a well-defined mechanical environment. In addition to these operating parameters (but outside the scope of this article), stringent EMC and noise requirements are specified to prevent any module from radiating enough energy into another module to affect its measurement integrity and reliability.

The VXI high-speed backplane and direct register access provide an environment for greater system throughput. The backplane also gives the user the ability to quickly reconfigure systems to provide design verification on a changing product mix. Furthermore, it provides an ideal environment for the user to develop a custom module for special-purpose measurements needed in hardware-in-the-loop design verification. For example, system designers can combine DSPs and high-speed analog-to-digital and digital-to-analog converters to act as a high-performance stimulus and measurement system for design verification.

The VXI backplane is defined around the popular VMEbus architecture, known for its excellent computer backplane. Along with the necessary communication protocols, the VXI backplane has high-speed data rates of 40 Mbytes/s. This makes it ideal for building instrument systems with high throughput and performance.

The VXI consortium has provided other resources for instrumentation. These include additional power-supply voltages for analog and ECL circuits, and instrumentation buses for measurement synchronization and triggering. Also included are an analog sum bus and a set of local bus lines for private module-to-module communication. A more-standardized set of communication protocols was developed for the VXIbus to handle autoconfiguration, resource management, and device communication. Some important specifications of the VXIbus that facilitate accelerated testing are described in the sidebar VXIbus Specifications Light The Way For Accelerated Testing.

As mentioned, the design of the ECM and its controlling firmware is a complex process, one that demands a fast coupling between the various VXI modules. Once the ECM is electrically designed, the architecture and optimization of the firmware that controls it must be verified. This really needs to be done in close coordination with the engine for which the ECM and its firm-ware are intended (Fig. 3). This is true in other applications as well—telecommunications, aerospace, military, and a world of other devices and systems.

The VXI specifications and backplane speed, along with the local bus, create a robust environment in which to build interdependent emulation of real-world signals that operate with various phases of a design. In the automotive application, the engine signals are emulated and brought to extreme circumstances, approaching what may not even be possible with a real engine. This is done so that the system pushes the firmware's work envelope. The goal in this case would be to uncover hidden faults that may exist just outside the boundaries of the real- world engine. In this situation, the VXI backplane throughput, along with the measurement and stimulus interoperability, provide a means to reach this area of verification, an area previously unattainable except in very rare circumstances.

An embedded VXI oscilloscope was also used in this system to capture elusive glitches. The high-speed digitizer measured voltage outputs and current inputs from the ECU, along with monitoring the outputs from the engine emulator itself.

The measurements then provided a map that identified the faults as they related to changes in various environmental or operational variables. The information gleaned from the state of the device during this process provided a greater understanding of the fault spectrum than had been previously known. The end result was a more-informed and quantitative means to select the best designs. Design verification with accelerated testing using a VXI system provides a pathway for higher quality, reduced design costs, and ultimately more satisfied customers.

In the VXI architecture, the VXI backplane directly connects to the measurement and computation subsystems (Fig. 4). It is this tight coupling of the embedded controller and measurement subsystem that allows a design engineer to span the measurement spectrum. The ability of the VXI architecture to make this jump is somewhat akin to a move from simple math functions like addition, subtraction, multiplication, and division, to the more-complex math functions of integrals and derivatives. Just as moving to higher forms of math provide paths to greater understanding, so too do systems that provide accelerated testing. They yield greater insight into the fault spectrum of newly designed devices.

VXIbus Specifications Light The Way For Accelerated Testing
The VXIbus is ideal for hardware-in-the-loop or accelerated design-verification testing. VXIbus specifies three 96-pin DIN connectors called P1, P2, and P3 (Fig. a). The P1 connector, the only mandatory connector in the VME or VXIbus, carries the data transfer bus (up to 24 bits addressing and 16 bits data), the interrupt buses, and some power.

The optional P2 connector, available on all card sizes except A, expands the data transfer bus to its full 32-bit size. It also adds many other resources including four additional power-supply voltages, the local bus, and the module-identification bus. The module-identification bus allows a VXIbus module's slot number to be determined via software control.

An optional P3 connector, available only on D-size, expands P2 resources for specialized applications. P3 pro vides 24 more local bus lines, additional ECL trigger lines, and 100 MHz clock and star trigger lines for precision synchronization.

The Local Bus adds significant capability to VXIbus measurement systems. It is a very-flexible, daisy-chain bus structure (Fig. b). In essence, every inner slot in a VXIbus mainframe has a set of very-short, pseudo 50-Ù transmission lines running between adjacent slots on either side. The local bus is 12 lines wide in each direction through the P2 connector, and an additional 24 lines wide through the P3 connector. This bus allows for adjacent modules to perform private communication. For example, a scanner module can multiplex a number of analog nodes to the input of a digital multimeter.

Each of these areas contribute to the ability to communicate between devices, VXIbus backplane, and controllers or computers as an integral part of any VXIbus test system. This communication can occur at the top speed of 40 Mbytes/s. Contrast this against the maximum data transfer rate of 1 Mbyte/s of IEEE-488. It is the backplane speed of the VXIbus that allows the system to be used in an accelerated test scheme.



VXIbus Manufacturers
Advanced Power Designs Inc.
17752 Skypart Cir. No. 240
Irvine, CA 92614
(714) 263-8605
fax (714) 263-8607
e-mail: [email protected]
http://www.vxibuff.com
ANA, ANS, MNF, PSU, SI, SOF,
SOU, SYS


Alphi Technology
6202 S. Maple Ave. No. 128
Tempe, AZ 85283
(602) 838-2428
fax (602) 838-4477
ANA, AVI, DAQ, DSP, ECC, SI, SOF, SYS

Analogic Corp.
8 Centennial Dr.
Peabody, MA 01960
(978) 977-3000
http://www.analogic.com
ANA, ANS, DAQ, SOF, SOU, SYN

Andor Design Corp.
20 Pond View Dr.
Syosset, NY 11791
(516) 364-1619
fax (516) 364-5428
MIL

Anritsu Wiltron
1155 East Collins Blvd.
Richardson, TX 75081
(800) ANRITSU
fax (972) 644-3416
e-mail: [email protected]
http://www.anritsu.com
ANA, DIG, DSP, MWV, SOU, SPA,
SSM, SYM


Ascor Inc.
47790 Westinghouse Dr.
Fremont, CA 94539-7485
(510) 490-2300
fax (510) 490-8493
[email protected]
http://www.ascor-inc.com
MWV, SI, SSM, SYM

ASSET InterTech Inc.
2201 N. Central Expwy. Suite 105
Richardson, TX 75080
(972) 437-2800
fax (972) 437-2826
e-mail: [email protected]
http://www.asset-intertech.com
AVI, BST, DIG, INT, SOF

B&B Technologies
6610 Golton Ct. NE Suite A
Abuquerque, NM 87109
(505) 345-9499
fax (505) 345-9699
e-mail: [email protected]
SI, SOF

B+K Precision
1031 Segovia Cir.
Placentia, CA 92870
(800) 462-9832
e-mail: [email protected]
http://www.bkprecision.com
DIG, PSU, SPA

Berkeley Nucleonics Corp.
3060 Kerner Blvd. No. 2
San Rafael, CA 94901
(800) 234-7858
(415) 453-9955
fax (415) 453-9956
e-mail: [email protected]
http://www.berkeleynucleonics.com
DAQ

BMC Communications Corp.
2 N. Nancy Pl.
N. Massapequa, NY 11758
(718) 575-1936
fax (718) 544-3628
e-mail: [email protected]
http://www.bmccorp.com
AVI, MIL, SI

CAL-AV Labs Inc.
1802 West Grant Rd., Ste. 116
Tuscon, AZ 85745
(888) 815-0400
(520) 624-1300
fax (520) 624-1311
e-mail: [email protected]
http://www.cal-av.com
CUS, DAQ

C&H Technologies Inc.
P.O. Box 14765
Austin, TX 78761-4765
(512) 251-1171
fax (512) 251-1963
e-mail: [email protected]
http://www.chtech.com
ANA, ANS, AVI, CUS, FRE, MIL,
MNF, SI, SOU, SSM, SYN, SYS, TRA


Circuit Equipment Corp.
ATE Div.
3511 Lost Nation Rd.
Willoughby, OH 44094
(440) 951-8840
fax (440) 951-5216
e-mail: [email protected]
http://www.bblink.com/cec/
ANA, CUS, DAQ, ECC, SI, SLT

Communication Techniques Inc.
9 Whippany Rd.
Whippany, NJ 07981
(973) 884-2580
fax (973) 887-6245
e-mail: [email protected]
http://www.cti-inc.com
ANA, AVI, DIG, FRE, MWV, SOU, SYN

Corelis
12607 Hidden Creek Way
Cerritos, CA 90703
(562) 926-6727
fax (562) 404-6196
e-mail: [email protected]
http://www.corelis.com
AVI, BST, CUS, DIG, DSP, ECC, INT,
MIL, SI, SOF SYS


Cubic Communications Inc.
9535 Waples St.
San Diego, CA 92121-2953
(619) 643-5800
fax (619) 643-5803
http://www.cubiccomm.com
ANA, DSP, FRE

Cytec Corp.
2555 Baird Rd.
Penfield, NY 14526
(800) 346-3117
fax (716) 381-4740
fax (716) 381-0475
[email protected]
ANA, AVI, BST, CUS, DAQ, DIG, INT,
MNF, MWV, SOF, SSM, SYS


EIP Microwave Inc.
1745 McCandless Dr.
Milpitas, CA 95035
(408) 945-1477
fax (408) 945-0977
[email protected]
http://www.eipm.com
MWV, SOU, SYN, SYS

Frequency Devices Inc.
25 Locust St.
Haverhill, MA 01830
(978) 374-0761
fax (978) 521-1839
e-mail: [email protected]
http://www.freqdev.com
ANA, AVI, DAQ

Carlo Gauazzi, Inc.
10 Mupac Dr.
Brockton, MA 02301
(508) 588-6110
fax (508) 588-0498
e-mail: [email protected]
ECC, PSU, SI, SYS

GenRad Inc.
7 Technology Park Dr.
Westford, MA 01886-0033
(978) 589-7000
fax (978) 589-7007
http://www.genrad.com
ANA, ANS, AVI, BST, CUS, DAQ, DIG,
ECC, FRE, MNF, SI, SLT, SOF, SYS


Hewlett-Packard Co.
Test and Measurement Org.
5301 Stevens Creek Blvd.
MS 54LAK
Santa Clara, CA 95052
(800) 452-4844 http://www.tmo.hp.com
ANA, ANS, AVI, CUS, DAQ, DIG, DSP,
ECC, FRE, INT, MIL, MNF, SI, SLT, SOF,
SOU, SPA, SSM, SYC, SYM, SYN, SYS


Highland Technology Inc.
320 Judah St.
San Francisco, CA 94122
(800) 73-4418
(415) 753-5814
fax (415) 753-3301
[email protected]
http://www.highlandtechnology.com
ANA, ANS, AVI, CUS, DAQ, DSP, ECC,
MWV, SOU, SSM, SYS


Hyperlabs Inc.
13830 S.W. Rawhide Ct.
Beaverton, OR 97008
(800) 354-9432
(503) 524-7771
fax (503) 524-6372
e-mail: [email protected]
http://www.hyperlabsinc.com
ANA, DAQ, DIG

ICS Electronics
473 Los Coches St.
Milpitas, CA 95035
(408) 263-5500
fax (408) 263-5896
e-mail: [email protected]
http://www.icselect.com
CUS, DIG, ECC, SI, SYS

ILC Data Device Corp.
105 Wilbur Pl.
Bohemia, NY 11716
(516) 567-5600 x7383
e-mail: [email protected]
ANS, AVI, DAQ, DIG, INT, MIL, SI,
SOF, SOU, SYM, SYN


Ines Inc.
14 Inverness Dr. E
C-230
Englewood, CO 80112
(303) 649-9024
fax (303) 649-9025
e-mail: [email protected]
http://www.inesinc.com
DAQ, SYM, SLT, SOF

KEY
ANA: Analog measurement
ANS: Analog sources
AVI: Avionics test
BST: Boundary-scan test
CUS: Custom circuits
DAQ: Data acquisition
DIG: Digital test
DSP: Digital signal processing
ECC: Embedded controllers/
computers
FRE: Frequency standards
INT: Interconnect devices
MIL: MIL-STD, Arinc, IRIG
MNF: Mainframes and accessories
PSU: Power supplies, controls, loads
SI: System integrator services
SLT: Slot 0 cards and IEEE-488 interfaces
SOF: Software
SOU: Sources
SSM: Switches, scanners, and multiplexers
SYC: Synchro/resolver instruments
SYM: System monitoring
SYN: Synthesizers
SYS: Systems
TRA: Transient recorders

VXIbus Manufacturers
Information Transfer Inc.
76 N. Maple Ave.
Ridgewood, NJ 07450
(201) 251-7700
fax (201) 251-8787
e-mail: [email protected]
http://www.info-transfer.com
ANA, AVI, DAQ, DIG, MIL, MNF, MWV,
PSU, SI, SLT, SOU, SPA, SSM, SYM, SYN


Instrumentation Engineering
415 Hamburg Tpke.
Wayne, NJ 07470-2134
(973) 389-0801
fax (973) 389-0913
e-mail: [email protected]
http://www.ATE-Solutions.com
ANA, ANS, AVI, BST, CUS, DAQ, DIG, SI,
SOF, SYM, SYS


Interface Technology Inc.
300 S. Lemon Creek Dr.
Suite A
Walnut, CA 91789
(909) 595-6030
fax (909) 595-7177
e-mail: [email protected]
http://www.interfacetech.com
AVI, BST, CUS, DIG, ECC, SLT, SOF, SYS

Kinetic Systems Corp.
900 N. State St.
Lockport, IL 60441
(815) 838-0005
fax (815) 838-4424
[email protected]
http://www.kscorp.com
ANA, ANS, AVI, CUS, DAQ, DIG, DSP, ECC,
INT, MIL, MNF, PSU, SI, SLT, SOF, SOU, SSM,
SYM, SYN, SYS, TRA


MAC Panel Co.
551 W. Fairfield Rd.
High Point, NC 27264
(336) 861-3100
fax (336) 861-6280
e-mail: [email protected]
http://www.macpanel.com
INT, MNF

ManTech International
ManTech Test Systems Div.
14119A Sullyfield Cir.
Second Floor
Chantilly, VA 20151
(703) 633-1300
e-mail: [email protected]
http://www.mantech.com
ANA, AVI, BST, CUS, DAQ, DIG, ECC,
MNF, MWV, PSU, SI, SLT, SOF, SPA, SSM,
SYC, SYM, SYN, SYS


MicroSignal Technology Inc.
80 Burr Ridge Pkwy., Unit 107
Burr Ridge, IL 60521
(800) 484-5339
(630) 325-8173
fax (630) 325-8306
email: [email protected]
http://www.microsignal.com
ANA, DSP

National Instruments Corp.
6504 Bridge Point Pkwy.
Austin, TX 78730
(512) 794-0100
fax (512) 794-8411
[email protected]
http://www.natinst.com
ANA, ANS, DAQ, DIG, ECC, MNF, SLT,
SOF, SOU, SSM, SYM


NH Research
16601 Hale Ave.
Irvine, CA 92606
(949) 474-3900
fax (949) 474-7062
http://www.nhresearch.com
PSU, SI, SLT, SSM, SYS

Noise Com Inc.
E. 64 Midland Ave.
Paramus, NJ 07652
(201) 261-8797
fax (201) 261-8339
[email protected]
http://www.noisecom.com
SOU

North Atlantic Instruments
170 Wilbur Pl.
Bohemia, NY 11716-2416
(516) 567-1100
fax (516) 567-1823
e-mail: [email protected]
http://www.naii.com
ANA, ANS, AVI, CUS, DAQ, FRE, PSU, SYC

Pentek
1 Park Way
Upper Saddle River, NJ 07458
(201) 767-7100
fax (201) 818-5941
e-mail: [email protected]
http://www.pentek.com
DAQ, DSP

QLOG Corp.
33 Standen Dr.
Hamilton, OH 45015
(513) 874-1211
fax (513) 874-1903
http://www.qlog.com
ANS, CUS, DSP, SI

Racal Instruments Inc.
4 Goodyear St.
Irvine, CA 92618
(800) 722-2528
(714) 859-8999
fax (714) 859-7139
http://www.racalinst.com
ANA, ANS, AVI, CUS, DAQ, DIG, ECC,
FRE, INT, MIL, MNF, MWV, PSU, SI, SLT,
SOF, SOU, SSM, SYM, SYN, SYS


Schroff Inc.
170 Commerce Way
Warwick, RI 02886
(401) 732-3770
fax (401) 738-7988
http://www.schroffus.com
PSU, SYS

Serendipity Systems Inc.
299 Van Deren
P.O. Box 10477
Sedona, AZ 86339
(520) 282-6831
fax (520) 282-4383
http://www.serendipsys.com
DIG, SOF

Spectrum Signal Processing
Suite 100
8525 Baxter Pl.
Burnaby, BC
Canada V5A 4V7
(604) 421-5422
fax (604) 421-1764
[email protected]
http://www.spectrumsignal.com
DSP

SIS GmbH
Moorhof 2d
22399 Hamburg
Germany
49 (0) 40 60 87 305 0
fax 49 (0) 40 60 87 305 20
e-mail: [email protected]
http://www.struck.de
CUS

Tektronix Inc.
Measurement Div.
P.O. Box 1520
Pittsfield, MA 01202
(800) 426-2200
http://www.tek.com/Measurement
ANA, ANS, AVI, BST, DAQ, DIG, DSP,
ECC, INT, MIL, MNF, SLT, SOF, SOU, SSM,
SYM, SYS, TRA


Teradyne Inc.
Assembly Test—Boston Div.
179 Lincoln St.
Boston, MA 02111
(617) 482-2700
fax (617) 422-3440
http://www.teradyne.com
ANA, BST, DIG, SI, SOF, SYS

TTI Testron Inc.
41 Century Dr.
Woonsocket, RI 02895
(800) 262-4894
(401) 766-9100
fax (401) 766-9017
http://www.ttitestron.com
ANA, CUS, DAQ, DIG, INT, MNF, SOF

Virginia Panel Corp.
1400 New Hope Rd.
Waynesboro, VA 22901
(540) 932-3300
fax (540) 932-3369
http://www.vpc.com
INT

VMETRO Inc.
1880 Dairy Ashford
Suite 535
Houston, TX 77077
(281) 584-0728
fax (281) 584-9034
e-mail: [email protected]
http://www.vmetro.com
DIG, MNF, SYM

VXI Associates
718 Maine St., Suite 210
P.O. Box 9
Boonton, NJ 07005
(973) 299-8321
fax (973) 299-9757
e-mail: [email protected]
http://www.vxi.com
ANA, ANS, AVI, BST, CUS, DAQ,
DIG, DSP, ECC, FRE, INT, MNF, MWV,
PSU, SI, SLT, SOF, SOU, SPA, SSM,
SYC, SYM, SYN, SYS, TRA


VXI Technology Inc.
17912 Mitchell
Irvine, CA 92714
(714) 955-1894
fax (714) 955-3041
e-mail: [email protected]
http://www.VXITech.com
ANA, ANS, AVI, CUS, DAQ, DIG, ECC,
MIL, MNF, MWV, PSU, SI, SLT, SOF, SOU,
SSM, SYM


Wavetek Corp.
Test and Measurement Div. 9045 Balboa Ave.
San Diego, CA 92123
(800) 223-9885
fax (619) 565-9558
http://www.wavetek.com
ANA, ANS, SOU

Westar Corp.
11520 St. Charles Rock Rd.
St. Louis, MO 63044
(314) 298-8748
fax (314) 298-8067
http://www.westar.com
CUS, SI
KEY
ANA: Analog measurement
ANS: Analog sources
AVI: Avionics test
BST: Boundary-scan test
CUS: Custom circuits
DAQ: Data acquisition
DIG: Digital test
DSP: Digital signal processing
ECC: Embedded controllers/
computers
FRE: Frequency standards
INT: Interconnect devices
MIL: MIL-STD, Arinc, IRIG
MNF: Mainframes and accessories
PSU: Power supplies, controls, loads
SI: System integrator services
SLT: Slot 0 cards and IEEE-488 interfaces
SOF: Software
SOU: Sources
SSM: Switches, scanners, and multiplexers
SYC: Synchro/resolver instruments
SYM: System monitoring
SYN: Synthesizers
SYS: Systems
TRA: Transient recorders

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