Introduction
to Digital electronics,
The
use of digital and numerical systems is in great use, wide application,...
There is only to look around us, and in all applications,
The
explosion of microelectronics and the complex architecture of systems.
An
increasing number of machines (digital camera, car, washing machine, etc.) use
digital electronics.
Until
the microprocessor appeared, we found two major sectors in the field of digital
systems.
This
division has remained with the computer manufacturers where we still find:
•
Hardware Department
• Software or programming department
(software)
The
appearance of the microprocessor had the effect of diminishing the importance
of the material and of causing a shift of the means of processing of circuits
and signals to complex applications.
So
we are increasingly faced with programs and electronic applications that
surround the machine as closely as we could.
This
forces programmers to get to know the hardware better and better (hardware,
microcontrollers,....) to better
"paste " or develop the application with the program for electronic product development.
After
reducing the market for wired logic, the microprocessor went on to conquer the
low-frequency electronics.
It has entered a large number of sectors
(games, telecommunications, automatic, etc.).
The
increase in integration possibilities (number of transistors per mm2, with
technology 0.35 ยต m2 micron meter) leads to a new evolution.
Programmable
logic circuits (CPLD, FPGA,...) become affordable and possible.
The programming of small applications is
replaced by wired logic in these programmable and complex circuits.
This
evolution makes it possible to envisage an increase in the speed of processing
of functions.
So
far, the learning of logic has been done through the uncovering of the basic
logical functions contained in the integrated circuits of the 74xxx families,
of which we can see some types in Figure 1,
The
experiments were limited to the functions proposed by the manufacturers of
these circuits.
The
design of logical functions involving several of these circuits required a
consequent cabling, and the production of a large-area printed circuit.
Fig-1
The
experiments were limited to the functions proposed by the manufacturers of
these circuits.
The
design of logical functions combining several of these electronic circuits
necessitated a consequent cabling, the development and the realization of a
large surface printed circuit.
The
appearance of programmable logic devices (PLD), CPLD (PLD complex, fig 2)
Fig-2
Field
programmable Gate Array (FPGA), Figure 1-2, Page 3
has made it possible to overcome this
limitation. In fact, the user can create, in these circuits, all the logical
functions that he wishes with only limitations, the place available in the
chosen circuit and/or the speed of operation of it.
The
current size of these circuits allows the integration of a complete processor
system.
In
English, the abbreviation is SoPC (SOC System on Chip programmable).
The
development tools made available to the users must therefore allow to move from
the description of the behavior of a logical function to its wiring in the
circuit and that in the simplest possible way.
At
the beginning of the years 90, the description of the behavior of logical
functions was made by the use of "Hardware description" language.
Among
these, one can quote:
The
first generation of these languages allowed descriptions at the logical level.
There
were two languages:
•
The CUPL used in the years 1980 to 1994.
•
The ABEL (Advanced Boolean Equation language) language used in the years 1990
to 1998 this language was created by the company DATA I/O and used or imitated
by almost all developers of development tools for this type of circuit (XABEL
for XILINX, AHDL for Altera, PLD for OrCAD, XPLA for PHILIPS, etc...)
This
language is no longer being used.
The
increase in the complexity of programmable circuits has required language
permitting higher-level (behavioral) descriptions.
Two
languages appeared at the beginning of the years 1990 for the design of ASIC
circuits (specialized integrated circuit).
They imposed themselves from the middle 1995
for programmable logic circuits. This is:
•
The VHDL (Very High Speed integrated Circuit, Hardware Description language)
language that has been created for the development of complex logical
integrated circuits.
It owes its success, essentially, to its
standardization under the reference IEEE-107
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