A
ABEL (Advanced Boolean Expression Language) -
An early hardware description language developed for PLD-based designs.
Accelerator - A specialized piece of hardware
that speeds up a software-based task. Usually used for speeding up simulation.
Algorithm - A recipe for performing an operation
such as computing an average value.
Analog - A continuously varying signal. For
example, if an analog signal's range is from 0 to 5 volts, the signal can assume
any voltage within that range such as 1.2, 2.4, or 4.7 volts. Microprocessors and
microcontrollers usually cannot process analog signals directly and require conversion
by an A/D converter before they can process the signal.
Analog Simulation - Modeling or simulation
of an electro nic circuit using representations of the actual circuit voltages, currents,
and component values instead of simplified digital state representations.
Analog-to-Digital Converter (also A/D, ADC) -
An electronic circuit that converts a continuously varying signal (temperature, pressure,
voltage, etc.) into digital zeroes and ones that can be processed by a microprocessor
or microcontroller.
Analyzer, Logic - An instrument that allows
you to observe the behavior of digital signals in an embedded system.
ASIC (Application-Specific Integrated Circuit)
- A custom integrated circuit designed specifically for one end product or a
closely related family of end products.
ASIC Emulation (also Logic Emulation) - The
use of programmable circuits, usually based on FPGAs, to emulate the design of an
ASIC or an IC before it is built. ASIC emulation allows designers to check the operation
of a design before committing the time and money required to fabricate the IC. Emulation
serves the same purpose as simulationódesign verificationóbut is much
faster because it is based on hardware rather than software.
Assembler - A computer program that translates
from assembly language (a language programmers can read) into machine code (consisting
of just zeroes and ones) which a microprocessor can read.
Assembly Language (also Assembly Code) - A
simple computer programming language, specific to each microprocessor or microcontroller,
which has a direct, one-to-one correspondence between each assembly-language instruction
and the associated machine-code instruction.
ASSP (Application-Specific Standard Part) -
A complex integrated circuit designed to perform a narrowly defined task such as
video compression, sound generation, or telephone modem telephony.
Asynchronous - A circuit that operates independently
of any regular, periodic time-controlling mechanism such as a clock.
ATPG (Automatic Test Pattern Generation) -
The automatic creation of te st patterns or "vectors" used to verify the
operation of an electronic circuit. The "goodness" of a set of test vectors
is based on "fault coverage" or the ability of the set of test vectors
to identify any manufacturing or design defects in the circuit.
Autorouter - An EDA tool that can automatically
generate the thousands or millions of connecting lines between electronic components
on a pc board or inside of an integrated circuit.
B
Back Annotation - The updating of a circuit
design using simulation and other post-processing information that reflects implementation-dependent
characteristics of the design such as pin selection, component location, or parasitic
electrical characteristics.
Bandwidth - A measure of a circuit's ability
to carry or process information. More or greater bandwidth means more carrying capacity
or greater processing power, usually achieved at greater cost.
Behavioral Model - A high-level representation
of an electronic design that describes the behavior of various modules or subsystems
in the design, usually without regard to the underlying technology used to implement
the design.
Behavioral Compiler - An EDA tool that can
synthesize circuitry from a very high level description of the circuit's behavior.
BiCMOS (Bipolar, Complementary-Symmetry Metal Oxide
Semiconductor) - An integrated circuit fabrication technology that combines the
two major IC technologies, bipolar and CMOS, on one IC.
Bidirectional - A signal or port that can act
as either an input to or an output from an electronic circuit.
Binary - The base-2 number system almost universally
used by modern computers, microprocessors, and microcontrollers.
Bipolar - The original semiconductor manufacturing
process technology. Usually characterized by high-speed, high-power operation.
Block Diagram - A graphical representation
of a system using a very high level of abstraction.
Bit (contraction of Binary digiT) - One digit
in the base-2 numbering system used by virtually all modern computers, microprocessors,
and microcontrollers. A bit can have a value of either zero or one.
Board, Circuit (also pc board) - A thin card,
usually made from fiberglass or plastic, which is covered with copper lines and is
used to hold the various integrated circuits in an embedded system.
Bond-Out Chip - A special version of a microprocessor
or microcontroller which brings critical internal signals from inside the chip out
on special package pins so that developers can more easily observe what's happening
inside of the processor. Usually used to build In-Circuit Emulators (ICEs).
Boolean Algebra - A mathematical system developed
in the 1800s to express the philosophical logic of Aristotle which was coincidentally
ideal for the description of digital circuits 100 years later.
Breadboard - A hand-made system prototype built
as a proof of concept. In the early days of electronics (even before transistors
were invented), engineers actually mounted circuit components on blocks of wood;
hence the term "breadboard."
Buffer - An isolation circuit used to insulate
sensitive analog or digital circuits from higher-power or higher-current levels in
other portions of an electronic design. Often seen, for example as an I/O buffer
which separates the sensitive circuits inside of an IC from the signals on the circuit
board to which the IC is attached.
Bus - A group of two or more signals that carry
closely-associated signals in an electronic design.
Byte - A binary word consisting of eight bits.
When used to store a numeric value, a byte can represent a number from 0 to 255.
C
CAD (Computer Aided Design) - The overarching
generic term for all software tools that enable or aid in th e creation of engineered
systems. Sometimes, CAD refers only to the electronic versions of mechanical-drafting
tools. Sometimes, it refers to all such tools including EDA tools.
CAE (Computer Aided Engineering) - The original
term for electronic design automation (EDA). Now, often refers to the software tools
used to develop the manufacturing tooling for the production of electronic systems
such as for the panelization of circuit boards.
CFI (CAD Framework Initiative) - A consortium
of EDA tool companies tasked with the development of framework standards for EDA
tools.
CISC (Complex-Instruction-Set Computer) - A
design approach for microprocessors and microcontrollers which employs relatively
complex instructions that execute over multiple clock cycles. A program written using
CISC instructions requires fewer such instructions to perform a task as compared
to a program written using RISC (Reduced-Instruction-Set Computer) instructions.
Clock - A master timing signal that sets the
operating pace of all other components in the embedded system.
Clock Skew - Variation from the ideal clock
timing across an entire electronic design (usually in an IC) caused by parasitic
elements. Seymour Cray was an early combatant of clock skew and had to design serpentine
traces on the Cray I supercomputer's circuit boards to compensate for clock skew.
Clock Tree - A tree-like configuration of circuitry
designed to minimize the effects of clock skew.
CMOS (Complementary Symmetry Metal Oxide Semiconductor)
- An IC process technology developed in the 1960s which typically runs at lower
power than bipolar circuitry. Early on, CMOS was much slower than bipolar but has
steadily gained in speed over the decades to rival today's bipolar speeds. Most ICs
are now made using CMOS technology.
Co-design - See Hardware/Software Co-design.
Compiler - A computer program which translates
programs written in an high-level language (HLL) into assembly-l anguage instructions
or machine code.
Concurrent Design - The ability to develop
many parts of a complex electronic design in tandem using EDA tools such as simulation
to stand in for portions of the system yet to be designed fully.
Concurrency - The ability of an electronic
circuit to do several (or at least two) different things at the same time. Contrast
with computer programs which usually execute only one instruction at a time unless
the program is running on a processor with multiple, concurrent execution units.
Controller - An electronic system that directs
the operation of some larger system.
Core - A predesigned block of logic employed
as a building block for ASIC design.
Co-simulation - Simulation of hardware and
software together, simultaneously.
Coverage - A measure of the "goodness"
of a test or test suite. Usually refers to fault coverage and is expressed as a percentage
of the circuit covered by the test. Usually, it is too expen sive to achieve 100%
coverage and test engineers shoot for coverage in the high 90s. Scan-test technology
can improve coverage results, at the expense of additional silicon on the chip and
some additional design time.
Crosstalk - A condition where signal activity
on one wire in an electronic circuit couples to another wire and causes noise through
electrostatic (capacitive) or electromagnetic (inductive) coupling.
CPLD (Complex Programmable Logic Device) -
A programmable IC which is more complex than the original Programmable Logic Devices
such as AMD's (originally MMI's) PALs but somewhat less complex than Field Programmable
Logic Arrays.
CPU (Central Processing Unit) - The core circuitry
of a computer including the ALU (arithmetic logic unit), address-control circuitry,
and bus-control circuitry. Usually implemented with a microprocessor or microcontroller
in an embedded system.
CUPL - A hardware description language originally
developed for PLDs.
D
Debugging - The art of finding and eliminating
errors in system designs.
Design Capture (also Design Entry) - The process
of entering an electronic system design into a computer using EDA tools.
Design Error - An flaw designed into an electronic
circuit which is then faithfully reproduced in every manufactured system (as opposed
to a manufacturing error which is a flaw created by the manufacturing process itself).
Emulation, simulation, and design-rule-checking tools all help to minimize or eliminate
design errors.
Design Rule Check - Verification of an IC or
pc board layout for conformance to the physical or electrical limitations of the
implementation technology in use.
DFT (Design for Test) - A design methodology
that includes special attention to the design of a circuit and the addition of special
circuitry that eases the testing of that design.
Digital - An approach to circuit design based
on the binary number system. Signals in digital circuitry can only assume well-defined
levels; intermediate levels are invalid. For example, in a digital system with a
signal range of 0 to 5 volts, the digital signal may have the logical value of 0
if the signal voltage is within the range of 0 to 0.5 volts and a logical value of
1 if the signal voltage is within the range of 2 to 5 volts. Signal voltages of between
0.5 and 2 volts are invalid and are not allowed.
Digital Simulation - A computer simulation
of an electronic circuit that uses simple Boolean or logic states to represent the
instantaneous state of the circuit. Because the representation is simplified from
the actual voltage and currents present in the circuit, digital simulation is much
faster than analog simulation.
Digital-to-Analog Converter (also D/A and DAC)
- A circuit that translates a signal from a numeric, digital representation used
by microprocessors and microcontrollers into an an alog signal.
Documentation - All of the paper and electronic
documents supplied with a component or system which are absolutely critical to fully
utilizing the product. For embedded-systems designers and developers, there is never
enough documentation.
DRC - See Design Rule Check.
DSP (Digital Signal Processor or Digital Signal
Processing) - A specialized microprocessor or electronic system designed to be
very fast at processing continuous signals such as sound and video.
E
EDA (Electronic Design Automation) - A large
collection of software tools that enhance and aid in the development of complex electronic
systems.
EDIF (Electronic Design Interchange Format) -
A standard representation format for describing electronic circuits, used to allow
the interchange of circuit design information between EDA tools.
EEPROM (Electrically-Erasable Programmable Read
-Only Memory) - An integrated circuit that stores programs and data in many embedded
systems. EEPROM stores retains information even when the power is off. Early EEPROM
was expensive on a cost-per-bit basis and was infrequently used. Newer "Flash"
EEPROM is much less expensive and its cost-per-bit approaches that of DRAM making
Flash EEPROM a very attractive memory device for embedded-systems design.
EMI (Electromagnetic Interference) - Noise
generated by electronic systems which can interfere with other electronic systems
by traveling through the air, over communications wires, and through power wiring.
Emulator (also ICE or In-Circuit Emulator) -
A complex, expensive, and often balky electronic system that simulates the presence
of an embedded-system's microprocessor or microcontroller. Used often and extensively
in the development and debugging of embedded-system programs.
EPROM (Erasable Programmable Read-Only Memory,
also UVEPROM) - An integrated circuit that stores p rograms and data in many
embedded systems. EPROM can only be programmed once. To erase an EPROM's contents,
it must be exposed to intense ultraviolet light for many minutes.
ESDA (Electronic System Design Automation) -
High-level EDA tools used to design and describe entire electronic systems.
Event - A point in time where a change occurs
in the state of an electronic circuit.
Event-Driven Simulator - A simulator that only
calculates circuit conditions when events (changes) such as the start of a new clock
cycle occur in the state of the system. In contrast, timing simulation computes the
state of a system using elapsed time (usually in nanoseconds or picoseconds).
F
Fast Prototype - A working product model built
quickly to try out product concepts. May lack the fit, finish, and complete capabilities
of the planned final product while still giving users an idea of how th e product
will work. Often assembled specifically for a conference or other dog-and-pony show.
Fault - An actual problem in an electronic
circuit that disables or degrades the performance of the circuit. Also, for EDA purposes,
a point in the circuit where a potential flaw could damage the circuit's operation.
Fault Coverage - The percentage of potential
faults identified and tested by a test program or suite of test programs. If the
tests can uncover all potential faults, the fault coverage for those tests is 100%.
Fault Simulation - Simulation of the operation
of an electronic circuit with the introduction of simulated manufacturing faults
to determine the amount of fault coverage provided by a set of test vectors. These
test vectors are then used to test the actual manufactured circuit so they must be
able to identify a large percentage of the possible manufacturing faults.
Finite Element Modeling - A relatively complicated
numerical method (computer algorithm) t hat can model complex electrical phenomena
such as electromagnetic wavefront propagation.
Floorplanning - The task of determining where
each major block of circuitry will go within an IC design.
FPGA (Field Programmable Gate Array) - An integrated
circuit containing a large number of logic cells or gates that can be programmably
configured after the IC has been manufactured. Some FPGAs use fuses for this programming
and others store the configuration in an on-chip EEPROM or RAM memory. Fuse-programmed
parts cannot be reprogrammed so they can only be configured once. EEPROM-based FPGAs
can be erased and reprogrammed so they can be configured many times. RAM-based FPGAs
can be reconfigured quickly, even while the circuit is in operation.
Framework - A unifying graphical user interface,
database format, and inter-tool communication scheme which allow a user to combine
EDA tools from various vendors to create a desired tool suite for the design of electronic
systems.
G
GaAs (Gallium Arsenide) - A high-speed IC process
technology that does not use silicon. Instead, GaAs uses the semiconductor element
Gallium doped with the impurity Arsenic. GaAs process technology currently produces
the fasted ICs possible but advanced CMOS processing has greatly reduced the speed
gap in the past few years. GaAs is most often used today for very high frequency
radio circuits such as the transmitter circuits in cellular phones.
Gate Array - A type of ASIC in which the transistors,
gates, and other active circuit elements are fixed on a wafer called a "master
slice." The customization for a particular application is done using the metal
interconnection layers on the chip. Thus, the IC vendor can fabricate and stockpile
master slices well in advance of a customer order and then fininsh the fabrication
by adding the metal layer or layers when the order is received. Because of this style
of fabrication, gate arrays are the easiest ASICs to design and offer the fastest
turnaround time between order and shipment of the finished parts. In the extreme,
Chip Express offers laser-programmed gate arrays with 24-hour turnaround time (or
less if you really have the money.)
Gbyte (gigabyte) - 1,073,741,824 bytes.
GDS II - A photoplotting file format usually
employed for integrated circuit mask plotting files. Originally developed by GE Calma,
an early EDA vendor.
Gerber Photoplot (or Gerber File) - A de-facto
file format standard originally developed for Gerber Scientific for its line of photoplotters.
Usually used for representing printed-circuit board designs.
Ground Bounce - Noise signals coupled into
the grounding network of an electronic system which cause a variety of operating
problems in the circuit.
H
Hard Macro - A relatively complex block of
l ogic or "core"ósuch as a multiplier or an entire microprocessoróthat
has been completely predesigned for use on a particular ASIC or FPGA technology.
Generally, a hard macro cannot be edited except by the company that created it. In
exchange for this relative lack of flexibility, hard macros usually provide better
performance using a smaller amount of silicon when compared to a "soft macro"
or "synthesizable core."
Hardware/Software Co-design - The simultaneous
development of product hardware and software. This design approach is more difficult
than a serial design which first develops the hardware and then the software that
will run on the hardware but the benefit is a reduced time to market. To develop
software before hardware is ready, software developers often create a behavioral
model of the hardware which can run the software and thus prove its function.
HDL (Hardware Description Language) - A synthetic
computer-based language used for the formal description of electronic circuits. An
HDL can describe a circuit's operation, its design, and a set of tests to verify
circuit operation through simulation. The two most popular digital HDLs are VHDL
and Verilog. An analog HDL called AHDL is under development by many vendors. HDLs
make it easier to develop very large designs through formal software engineering
methods that define ways to divide a large team project into smaller pieces that
can be implemented by individual team members.
Hierarchy - A method for describing and modeling
an electronic system using different abstraction levels. At the bottom level of the
hierarchy is the actual physical layout of the design (a concrete level, not at all
abstract). At the top of the hierarchy is a functional description of the system
or a block diagram (a very high level of abstraction). Intermediate levels include
the register-transfer level (RTL), the gate level, and the transistor level.
HLL (High-Level Language) - A relatively complex
computer programming language that all ows the programmer to work at a mathematically
abstract level instead of the low, physical level of the microprocessor or microcontroller.
For example, instead of dealing directly with registers and memory locations, the
HLL programmer works with variables and arrays. Java, C, Pascal, Fortran, and BASIC
are all examples of high-level languages.
I
IBIS (I/O Buffer Information Specification) -
A standard simulation format used to model the behavior of an integrated circuit's
input/output (I/O) pins. Used in designing and simulating the operation of circuit
buses.
IC (Integrated Circuit) - A silicon chip containing
hundreds, thousands, or millions of circuit elements such as transistors, resistors,
capacitors, and inductors. RAM, ROM, microprocessors, and microcontrollers are all
examples of integrated circuits.
I/O (Input/Output) - The wide range of circuits
and sensors used to bring information into an embedded-system processor and to transport
processed information back out of the processor. Serial and parallel ports, keyboard
and keypad controllers, floppy and hard disk drives, and displays are all examples
of I/O devices.
K
Kbyte (kilobyte) - 1024 bytes.
L
Linear - See Analog.
Logic - Digital circuitry, whether in an IC,
an ASIC, a microprocessor, or a microcontroller.
Logic Emulation - See ASIC Emulation.
Logic Synthesis - See Synthesis.
M
Mbyte (megabyte) - 1,048,576 bytes.
MCM (Multi-Chip Module) - A hybrid manufacturing
technique which places several IC chips into a single package. MCMs are a way of
"creating" an inte grated circuit using otherwise incompatible IC fabrication
technologies (such as CMOS and GaAs). MCMs are also a way of extending the reach
of existing ASIC technologies which may lack the ability to implement an entire system
design on one chip.
Microcontroller (also mC) - A real "computer
on a chip" incorporating a microprocessor, memory, and I/O circuits on one integrated
circuit. In many embedded systems, the microcontroller may well be the only integrated
circuit in the design.
Mixed-Mode - Operation in both the digital
and analog domains (usually refers to simulation as in "mixed-mode simulation").
Mixed-Signal - An electronic circuit that has
both analog and digital sections. Because many "real-world" systems have
analog interfaces (for example, most temperature, pressure, sound, and video sensors
are analog), most electronic systems must accommodate analog signals. However, signal
processing is now most efficiently performed by digital circuits. Therefore, almost
all m odern electronic systems are mixed-signal systems although individual ICs in
such systems need not be mixed-signal chips. Instead, a design can achieve mixed-signal
operation by combining separate analog and digital ICs.
Mixed-Signal Simulation - A simulation that
combines the abilities of an analog simulation and a digital simulation. Used to
verify the operation of mixed-mode circuitry.
Microprocessor (also mP) - The original "processor
on a chip" introduced by Intel in 1971. An integrated circuit that contains
all of the processing components of a computer CPU including the ALU, program sequencer,
and bus interface. Newer microprocessors also incorporate cache memory for increased
processing speed. Comes in 4-, 8-, 16-, 32-, and 64-bit varieties. Usually requires
other ICs to make up an embedded system.
Microprocessor Emulator - A piece of equipment
that substitutes in a circuit for the circuit's microprocessor. The emulator gives
more control over the circuit's operation a nd eases debugging and troubleshooting
efforts.
MIPS (Millions of Instructions Per Second) -
A performance figure of merit (numeric score or rank) for microprocessors and microcontrollers.
Moore's Law - An empirical law developed and
later revised by Intel's Gordon Moore which predicts that the IC industry is capable
of doubling the number of transistors on a silicon chip every 18 months (originally
every year) resulting in declining IC prices and increasing performance. Most design
cycles in the electronics industry including embedded-system development firmly rely
on Moore's law.
Multitasking - A programming style that splits
the overall job to be performed by the embedded system into a number of smaller tasks
which then execute on the system's processor in a time-shared fashion.
N
Nanosecond - One billionth of a second.
Net - 1. For ASICs, an individual sig nal path
including all of its branches and extensions. 2. An abbreviation for the Internet.
Net Extraction - The identification and cataloging
of all signal paths in a circuit. The combination of all nets and circuit elements
(transistors, resistors, capacitors, ICs, etc.) of an electronic design completely
describes an electronic circuit.
Net List (or Netlist) - A computer file (sometimes
a printed listing) containing a list of the signals in an electronic design and all
of the circuit elements (transistors, resistors, capacitors, ICs, etc.) connected
to that signal in the design.
Network Simulation - Simulation of a communications
network to determine if it has the desired communications capacity, noise insensitivity,
and fault tolerance.
Node - A single point in an electronic circuit.
O
Object-Oriented Programming - A programming
style that combines data bl ocks and the associated software processing algorithms
into "encapsulated" modules with narrowly defined entry and exit points.
This programming style was developed as a way of dealing with extremely large and
complex software programming projects by breaking the project down into smaller chunks
more easily handled by an individual programmer. The narrowly defined entry and exit
points of each module prevent one programmer's module from disrupting another's.
P
PAL (Programmable Array Logic) - The first
truly successful family of programmable logic, originally introduced by Monolithic
Memories in the early 1980s.
PALASM (PAL Assembler) - The HDL originally
developed by John Birkner of Monolithic Memories for the creation of PAL-based designs.
Patch - A small piece of code used to repair
an error in an existing embedded system program.
PCB (printed circuit board, pc board, als o PWB
or Printed Wiring Board) - A laminated board made from alternating layers of
copper and plastic (usually impregnated with glass fibers for strength). The pc board
serves as the physical carrier for other electronic components in an electronic design
and also provides the electrical connection between these electronic components.
PGA (Pin Grid Array) - A type of IC package,
usually square, with many interconnection pins (often hundreds).
Picosecond - One trillionth of a second.
Place and Route - A layout task that positions
major functional blocks or electronic components within an IC or on a pc board (Place)
and the subsequent routing of appropriate electrical connections to those components
(Route).
Platform - Market speak for a computer, operating
system, or framework.
PLCC (Plastic Leaded Chip Carrier) - A low-cost
IC package (usually square). PLCCs have interconnection leads on either two (usually
only for memory chips) or all four sides (f or logic and ASIC chips).
PLD (Programmable Logic Device) - The generic
term for all programmable-logic ICs including PLAs (programmable logic arrays), PALs,
CPLDs (complex PLDs), and FPGAs (field programmable gate arrays).
Point Tool - Market speak for an EDA tool that
performs only one function.
Power Simulation - A simulation that determines
the power consumption of an electronic circuit operating under a variety of normal
and abnormal conditions.
Price Point - Market speak for price. Adapted
from the consumer markets where there really is a difference in sales between products
priced at $9.99 and $10.
PROM (Programmable Read-Only Memory) - An integrated
circuit that stores programs and data in many embedded systems. PROM stores retains
information even when the power is off but it can only be programmed or initialized
once.
R
RAM (Random-Access Memory) - An integrated
circuit that stores programs and data in many embedded systems. RAM does not retain
information when the power is off and must therefore be reinitialized every time
the embedded system is switched on. There are many varieties of RAM including the
two most popular types: Dynamic RAM (DRAM) and Static RAM (SRAM).
RC Extraction - The mathematical computation
of an electronic circuit's fundamental circuit elements: resistors (abbreviated R),
and capacitors (abbreviated C). RC extraction allows a simulator to determine the
expected behavior of the electronic circuit through the mathematical modeling of
simple circuit elements.
Register - A location inside of a microprocessor,
microcontroller, or I/O controller chip that stores control or status information.
RISC (Reduced-Instruction-Set Computer) - A
design approach for microprocessors and microcontrollers, originally developed at
IBM, which employs relatively simple instructions that usually execute in one cloc
k cycle. This approach results in a faster, simpler processor design that uses fewer
transistors. However, a program written using RISC instructions requires more instructions
to perform a task as compared to a program written using CISC (Complex-Instruction-Set
Computer) instructions.
ROM (Read-Only Memory) - An integrated circuit
that stores programs and data in many embedded systems. PROM stores retains information
even when the power is off but it can only be programmed or initialized once and
only at the semiconductor factory.
ROM Emulator - An embedded-system development
tool that substitutes RAM for program ROM and aids in the debugging of the program.
RTL (Register Transfer Level or Register Transfer
Logic) - A register-level description of a digital electronic circuit (see "Hierarchy").
Registers store intermediate information between clock cycles in a digital circuit,
so an RTL description describes what intermediate information is stored, where it
is stored within t he design, and how that information moves through the design as
it operates.
S
Scan - A specialized test approach that places
special shift-register circuits inside of an electronic design just for test purposes.
The shift register allows automatic test equipment to introduce test patterns deep
into the circuitry and to read out status information that results from the circuit's
response to those test patterns.
Schematic - A graphical representation of an
electronic circuit. Until the 1980s, schematics were really the only representation
system used to describe circuits. However, with the advent of HDLs and an explosion
in circuit complexity, schematics are becoming less important as a representation
tool.
Schematic Entry - The process of drawing a
schematic using EDA tools. When done with paper and pencil, schematic entry is called
schematic drafting or schematic drawing.
S CSI (Small Computer System Interface, pronounced
"scuzzy") - An eight-bit parallel computer peripheral interface standard
used to connect to a wide variety of peripherals devices including hard-disk and
CD-ROM drives, tape-backup units, and optical scanners.
Simulation - Modeling of an electronic circuit
(or any other physical system) using computer-based algorithms and programming. Simulations
can model designs at many levels of abstraction (system, gate, transistor, etc.).
Simulation allows engineers to test designs without actually building them and thus
can help speed the development of complex electronic systems. However, the simulations
are only as good as the mathematical models used to describe the systems; inaccurate
models lead to inaccurate simulations. Therefore, accurate component models are essential
for accurate simulations.
Simulation Model - A software representation
of a system component that describes how that component operates under various electrical
and physica l (temperature, pressure, light, etc.) stimulus.
Soft Macro - A predefined block of logic (such
as a multiplier or microprocessor), which can be used as a building block for creating
ASIC designs. In contrast to "HardMacro"s, soft macros can be decomposed
into component-level parts and edited for a particular application.
SPICE (Simulation Program with Integrated Circuit
Emphasis) - The granddaddy analog simulation program developed at the University
of California at Berkeley in the early 1970s.
SRAM (Static Random-Access Memory) - An integrated
circuit that stores programs and data in many embedded systems. SRAM does not retain
information when the power is off and must therefore be reinitialized every time
the embedded system is switched on. SRAM is more expensive than DRAM on a cost-per-bit
basis but is usually easier to connect to a microprocessor or microcontroller.
Standard Cell - A form of ASIC design that
employs predefined logic cells and circuit component s to create an ASIC. All mask
layers of a standard-cell ASIC are custom for that ASIC, in contrast to a "Gate
Array" in which only the metal-layer masks are custom. Standard-cell ASICs usually
run faster and use less silicon (and are therefore usually cheaper on a per-part
basis) than Gate Arrays. However, because the standard-cell ASIC uses predefined
circuit components, its usually easier to design (and therefore requires less time
to design) than a full-custom ASIC where every resistor, capacitor, and transistor
is custom built.
State Diagram - A graphical representation
of a state machine's operation. State-diagram editors are EDA tools specifically
design to aid in the development of state machine designs.
State Editor - A design-entry EDA tool used
to create state diagrams.
State Machine - A digital circuit built from
registers and gates that controls the operation of other circuitry. For example,
microprocessors contain many state machines that sequence the flow of info rmation
over the processor's bus and through its data-manipulation circuits.
Static Timing Analyzer - An EDA tool that exhaustively
checks every signal path in a circuit to identify timing-related design problems.
Symbol - A graphic, schematic library element
that represents an electronic component such as a resistor, a capacitor, a transistor,
or an IC.
Symbol Editor - An EDA tool for maintaining
and creating schematic symbols.
Synchronous - A digital circuit where all of
the operations occur in lock step to a master clock signal.
Synthesis (also Logic Synthesis) - A computer
process that transforms a circuit description from one level of abstraction to a
lower level, usually towards some physical implementation. Synthesis is to hardware
design what compilation is to software development. In fact, logic synthesis was
originally called hardware compilation.
T
Test Synthesis - The automatic creation of
test patterns and a test program for the verification of manufactured ICs.
Test Vector - A stimulus pattern applied to
a circuit to verify the circuit's operation.
Timing Diagram - A graphical representation
of the signals in an electronic circuit that shows how the signals change over time
in relationship to each other.
Timing Simulation - Simulation of an electronic
circuit's operation over time using calculated circuit parameters such as resistance,
capacitance, inductance, and timing delays.
Transmission Line - A conductor or wire that
is suited to carrying high-frequency signals.
Top-Down Design - A design methodology that
starts the design of an electronic system at the very highest level of abstraction
and then methodically broadens the design through lower abstract layers until finally
reaching the concrete, physical design layer which accurately represents the implementation
technology for the system.
Twinkies - Critical nutrition for hardware
and software designers.
U
Unit Delay Simulation - A simplified form of
timing simulation where every digital gate is assumed to introduce one unit of delay
to a signal. In reality, different gates have different speeds, but unit delay simulation
trades off accuracy for simulation speed.
V
Verification - The task of establishing the
correctness of a design using EDA tools to automatically check the timing, connections,
and rules used to design the circuit.
Verilog - A hardware description language developed
by Gateway Design Automation (now part of Cadence) in the 1980s which became very
popular with ASIC and IC designers.
VHDL (VHSIC Hardware Description Language) -
A hardware description language developed in the 1980s by IBM, Texas Instruments,
and Intermetrics under US government contract for the Department of Defense's VHSIC
(Very High Speed Integrated Circuit ) program. VHDL enjoys a growing popularity with
ASIC designers as VHDL development tools mature.
W
Word - A unit of memory usually consisting
of two bytes (16 bits).
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