Page 34 - Engineering Digital Design

1.4 GLOSSARY OF TERMS, EXPRESSIONS, AND ABBREVIATIONS

1.3 A WORD OF WARNING

Not yet mentioned are the changes that must take place in the universities and colleges
to deal with this rapidly evolving technology. It is fair to say that computer aided design
(CAD) or automated design of digital systems is on the upswing. Those who work in the
areas of digital system design are familiar with such hardware description languages as
VHDL or Verilog, and the means to "download" design data to program PLAs or FPGAs
(field programmable gate arrays). It is possible to generate a high-level hardware description
of a digital system and introduce that hardware description into circuit layout tools such
as Mentor Graphics. The end result would be a transistor-level representation of a CMOS
digital system that could be simulated by one of several simulation tools such as HSPICE
and subsequently be sent to the foundry for chip creation. The problem with this approach to
digital system design is that it bypasses the need to fully understand the intricacies of design
that ensure proper and reliable system operation. As is well known, a successful HSPICE
simulation does not necessarily ensure a successful design. In the hands of a skilled and
experienced designer this approach may lead to success without complications. On the
other hand, if care is not taken at the early stages of the design process and if the designer
has only a limited knowledge of design fundamentals, the project may fail at one point
or another. Thus, as the use of automated (CAD) designs become more attractive to those
who lack design detail fundamentals, the chance for design error at the system, device,
gate, or transistor level increases. The word of warning: Automated design should never
be undertaken without a sufficient knowledge of the field and a thorough understanding of
the digital system under consideration — a little knowledge can be dangerousl This text is
written with this warning in mind. The trend toward increasing CAD use is not bad, but
automated design methods must be used cautiously with sufficient background knowledge
to carry out predictably successful designs. Computer automated design should be used
to remove the tedium from the design process and, in many cases, make tractable certain
designs that would otherwise not be possible. But CAD is not a replacement for the details
and background fundamentals required for successful digital system design. It is the goal
of this text to provide the reader with the necessary details and background fundamentals
so as to permit a successful transition into the CAD domain.

1.4 GLOSSARY OF TERMS, EXPRESSIONS, AND ABBREVIATIONS

Upon entering any new field, there is always the problem of dealing with the "jargon" that
is peculiar or unique to that field. Conspicuously absent in most texts on digital design is a
glossary of terms, expressions, and abbreviations that are used — yes, and even overused —
in presenting the subject matter. Readers of these texts are often left leafing through back
pages and chapters in search of the meaning of a given term, expression or abbreviation.
In breaking with tradition, this text provides an extensive glossary, and does so here at the
beginning of the text where it can be used — not at the end of the text where it may go
unnoticed. In doing this, Chapter 1 serves as a useful source of information.
ABEL: advanced Boolean expression language.
Accumulator: an adder/register combination used to store arithmetic results.
Activate: to assert or make active.