Friday, September 30, 2016

Embedded System Glossary – A

Embedded System Terminology - A

ABEL - The Advanced Boolean Expression Language (ABEL) is a Hardware description language and an associated set of design tools for programming PLDs.
Absolute Memory Address - The physical address of a specific memory cell.
Accumulator - A special processor register used in arithmetic and logical operations to store an operand used in the operation, as well as the results of the operation.
Acknowledge (ACK) - A signal used in bus and network “handshaking” protocols as an acknowledgment of data reception from another component on the bus (on an embedded board for bus handshaking) or from another embedded system via some networking transmission medium (for network handshaking).
Active High - Where a logic value of “1” is a higher voltage than a logic value of “0” in a circuit.
Active Low - Where a logic value of “0” is a higher voltage than a logic value of “1” in a circuit.
Actuator - A device used for converting electrical signals into physical actions, commonly found in flow-control valves, motors, pumps, switches, relays and meters.
Adder - A hardware component that can be found in a processor’s CPU that adds two numbers.
Address Bus - An address bus carries the addresses (of a memory location, or of particular status/control registers) between board components. An address bus can connect processors to memory, as well as processors to each other.
Addressing Mode - The term addressing modes refers to the way in which the operand of an instruction is specified.
Ahead-of-Time Compiler (AOT) - See Way-Ahead-of-Time Compiler.
Aliasing - (1) Allowing one memory location or register to be accessible at more than one address. (2) An effect, because of undersampling, where a time-varying signal appears to be running, at a much lower frequency than it really is. 3 Different variables reference the same physical memory location. In languages that support pointers, it is common for a program to maintain multiple references to the same storage. Each of these references is an alias.
Alternating Current (AC) - An electric current whose voltage source changes polarity of its terminals over time, causing the current to change direction with every polarity change.
Ammeter - A measurement device that measures the electrical current in a circuit.
Ampere - The standard unit for measuring electrical current, defined as the charge per unit time (meaning the number of coulombs that pass a particular point per second).
Amplifier - A device that magnifies a signal. There are many types of amplifiers (log, linear, differential, etc.), all differing according to what how they modify the input signal.
Amplitude - A signal’s size. For an AC signal it can be measured via the high point of an AC wave from the equilibrium point (center) to the wave’s highest peak or by performing the RMS (root mean square) mathematical scheme—which is by 1) finding the square of the waveform function, 2) averaging the value of the result of step 1) over time, and 3) taking the square root of the results of step 2). For a DC signal, it is its voltage level.
Amplitude Modulation (AM) - The transmission of data signals via modifying (modulating) the amplitude of a waveform to reflect the data (i.e., a “1” bit being a wave of some amplitude, and a “0” bit being a wave with a different amplitude).
Analog - Data signals represented as a continuous stream of values.
Analog-to-Digital Converter (A/D Converter) - A device that converts analog signals to digital signals.
AND Gate - A gate whose output is 1 when both inputs are 1.
Anion - A negative ion, meaning an atom that gains electrons.
Anode - (1) The negatively charged pole (terminal) of a voltage source. (2) The positively charged electrode of a device (i.e., diode), which accepts electrons (allowing a current to flow through the device).
Antenna - A transducer made up of conductive material (wires, metal rod, etc.) used to transmit and receive wireless signals (radio waves, IR, etc.).
Antialiased Fonts - Fonts in which a pixel color is the average of the colors of surrounding pixels. It is a commonly used technique in digital televisions for evening (smoothing) displayed graphical data.
Aperiodic - Lacking periodicity; random. The arrival of interrupts is often aperiodic.
Application Layer - The layer within various models (OSI, TCP/IP, Embedded Systems Model, etc.), which contains the application software of an embedded device.
Application Programming Interface (API) - A set of subroutine calls that provide an interface to some type of component (usually software) within an embedded device (OS APIs, Java APIs, MHP APIs, etc.).
Application Specific Integrated Circuit (ASIC) - An application-specific ISA-based IC that is customized for a particular type of embedded system or in support of a particular application within an embedded system. There are mainly full-custom, semi-custom, or programmable types of ASICs. PLDs and FPGAs are popular examples of (programmable) ASICs.
Architecture - See Embedded Systems Architecture or Instruction Set Architecture.
Arithmetic Logic Unit (ALU) - The component within a processor’s CPU, which executes logical and mathematical operations.
ARM - A 32-bit RISC processor widely used in low-power embedded applications.
ARM Thumb - A 16-bit variant of the 32-bit ARM instruction set. It can be fetched more quickly across a narrower data bus and consume less memory.
ARP - Address Resolution Protocol. A mechanism for mapping a destination IP address to its corresponding MAC address so that an IP packet can be routed over a specific physical network such as Ethernet.
Aspect Ratio - A ratio of width to height (in memory the number of bits per address to the total number of memory addresses, the size or resolution of a display, etc.).
Assembler - A compiler that translates assembly language into machine code.
Assembly Language - A human-writable form of a processor's native instruction set. The human-readable representation of each opcode is called a mnemonic.
Astable Multivibrator - A sequential circuit in which there is no state it can hold stable in.
Asynchronous - A signal or event that is independent of, unrelated to, and uncoordinated with a clock signal.
Atomic - An operation that cannot be interrupted is considered atomic.
Attenuator - A device that reduces (attenuates) a signal (the opposite of what an amplifier does).
Autovectoring - The process of managing interrupts via priority levels rather than relying on an external vector source.
Average Case execution time - The average amount of time to execute a section of code.

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Related topics:
Embedded System Architecture   |   Embedded Hardware Architecture   |   Embedded Software Architecture   |   Embedded Software Definition   |   Embedded System Acronyms   |   Embedded System Symbols

List of topics: Embedded System

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