Page 108 - Building A Succesful Board-Test Strategy

94 BUILDING A SUCCESSFUL BOARD-TEST STRATEGY

Monolithic ttsters are the machines traditionally associated with automatic
test equipment (ATE). These are single—often large—boxes from one vendor, con-
taining a computer engine and a collection of stimulus and measurement elec-
tronics. Measurement architecture is generally unique to that vendor, although
most vendors today use a standard computer engine, such as a PC-type or UNIX
workstation, to avoid developing and maintaining computer-bound system soft-
ware. The vendor defines the machine's overall capability. Customers must meet
additional requirements through individual instruments over a standard bus, such
as IEEE-488.
One advantage of the monolithic approach is that individual measurement
capabilities lack unnecessary features, such as front panels, embedded computer
functions, displays, and redundant software, that can make instrument-bound solu-
tions more awkward and more expensive. The vendor generally provides a well-
integrated software package and supports it directly, an advantage of "one-stop
shopping" for test-program development. The vendor is familiar with everv
part of the system and how the parts interact, permitting the most effective service
and support.
On the other hand, these systems are quite inflexible. If a customer wams
a capability that the tester does not already have, one option is IEEE-488
instruments. Expandability is limited to instruments and vendor offerings. A
functional tester may contain 256 pins, and the architecture may permit up to
512. The customer can expand to that point, but not beyond. The vendor may offer
other features as field upgrades, but only those features are available. Add-on instru-
ment choices are somewhat limited, and they often do not integrate well into system
software. Programming the instruments requires one of the "point-and-click"
programming tools or—as a last resort—that marvel of cryptic horrors, IEEE-488
language,
Ruck-und-stack systems consist of a computer engine, (usually a PC-type), a
switching matrix, and an array of instruments, communicating over a common S/O
bus such as IEEE-488. Rack-and-stack solutions permit purchasing appropriate
instruments from any vendor, as long as they support the communication bus.
Therefore, this solution provides the most flexible hardware choices. It may also
provide the best-quality hardware. The best switching matrix may come from
vendor A, the function generator and spectrum analyzer from vendor B, the wave-
form analyzer from vendor C, and the logic analyzer from vendor D. Because it
permits foregoing capability that the customer does not need, rack-and-stack
systems may be less expensive than monolithic or hybrid solutions.
Some vendors will act as consultants, helping customers to assemble rack-
and-stack systems from components, regardless of individual-instrument manu-
facturer. This is a handy service, as long as the vendor is honest about recom-
mending, purchasing, and pricing competitors' products.
For analog and high-frequency applications, rack-and-stack solutions are
often more accurate, less expensive, and easier to use than an array of instruments
attached to a monolithic tester. In addition, some capabilities are available only as