implemented by simply combining the proper MSI
Large Scale Integration (LSI)
LSI circuits are large and complex, and generally
contain circuitry equivalent to 100 or more typical
logic gates. LSI circuits are also functional in nature.
T y p i c a l L S I I C s i n c l u d e m e m o r i e s a nd
Very Large Scale Integration (VLSI)
VLSI circuits are large, complex circuits that
contain the equivalent of 1,000 or more logic gates.
Early digital computers use a mix of SSI MSI,
and LSI circuits. Over the years, the trend has been
toward the greater use of MSI, LSI, and VLSI circuits.
Today, most computers are predominately MSI, LSI,
and VLSI circuits. The SSI circuits are used only in
interfacing the other three larger and more
DIGITAL CIRCUIT CHARACTERISTICS
Many factors influence the choice of logic
circuits used to implement a digital computer. The
most important of these are speed, power dissipation,
and the availability of MSI, LSI, and VLSI circuits.
Other factors include the cost, noise immunity, and
The most important choice of a type of logic
involves speed and power dissipation. Speed refers to
the frequency of operation or propagation delay of the
logic circuits. The higher the speed of operation, the
greater the amount of data that can be processed in a
given time. Therefore, computer designers try to
achieve as much speed as possible in their designs.
Many high-speed circuits and techniques are
available. Besides choosing circuits with low
propagation delay times, circuit reduction techniques
are used to minimize propagation delay through
proper physical layout as well as logic simplification.
However, speed is always obtained at the expense of
increased power dissipation and cost. Invariably, the
designer faces a speed-power tradeoff, and attempts
to optimize the design for maximum speed within
realistic power consumption and cost guidelines.
Choosing ICs for use in a digital computer
involves not only choosing a specific logic family, but
also in choosing the correct mix of the various IC
By being flexible in the
circuit choice of mix, a designer can more easily
optimize the design.
This means freely mixing
different families of bipolar and MOS, as well as
VLSI, LSI, MSI, and SSI circuits.
For a detailed look at bipolar and MOS theory, as
well as more information on VLSI, LSI, MSI, and SSI
circuits, refer to Aviation Electronics Technician 2
(Intermediate), NAVEDTRA 12334, chapter 2.
Learning Objective: Recognize concepts and
procedures used in the construction of a
Computer programming is the process of
planning a solution to a problem. You can derive a
general outline for calculating total resistance of a
parallel resistance circuit by using the following
1. Take the reciprocal of the resistance in ohms
of all resistors in a circuit.
2. Calculate the sum of the values from step 1.
3. Compute the reciprocal of the value from
The process of preparing a program from this
explanation is not difficult. One basic charcteristic
of the computer must be considered-it cannot think.
It can only follow certain commands, which must be
correctly expressed and must cover all possibilities.
If a program is to be useful, it must be broken down
into specifically defined operations or steps. These
operations or steps, along with other data, must be
communicated to the computer in a language that it
The instructions are read
sequentially unless otherwise stated.
Generally, the steps that a computer follows in the
execution of a program are as follows:
1. Locates parameters (constants) and such data
as necessary for problem solving
2. Transfers the parameter and data to the point
3. Performs the manipulation according to
certain rules of logic