Glossary

AHB: Advanced High-performance Bus. Part of the AMBA specification for interconnectivity, the AHB is a single-cycle bus to which you normally attach bus masters, such as processor cores, DSP engines, DMA engines, or memory.

AMBA: Advanced Microcontroller Bus Architecture. The AMBA specification provides a bus framework around which systems can be built, and it also defines the manner in which processors and peripherals communicate in a system.

APB: Advanced Peripheral Bus. Part of the AMBA specification, the APB is the bus to which you normally attach peripherals or slower devices in the system.

API: Application Programming Interface. Often APIs come in the form of a library that includes routines for accessing hardware or services at a high level, resembling function calls.

ASIC: Application Specific Integrated Circuit. A description of any integrated circuit which is built for one specific purpose, as opposed to a generic device such as a microprocessor, which can be used in many applications. Examples are anti-lock disc brake circuits for a particular manufacturer or engine controllers for a particular vehicle.

Big-Endian: Byte-ordering scheme in which bytes of decreasing significance in a data word are stored at increasing addresses in memory.

Cache: From the French caché; literally, hidden. This memory, located very near the processor, holds recently used data and allows a processor to find data on the chip before going out to external memory, which is much slower.

CAN: Controller Area Network. Developed by Bosch and Intel, this is a network protocol and bus standard that allows automotive components like transmissions, engine control units, and cruise control to communicate as a subsystem within the car.

CISC: Complex Instruction Set Computer. An older computer architecture which implements a large instruction set, usually microcoded, and can have instructions of varying length.

Die: An individual square produced by cutting a wafer into pieces. Normally a die contains an entire microprocessor or analog device, including contact points (pads).

DSP: Digital Signal Processor. Any device which is specifically designed to transfer large amounts of data while providing arithmetic operations in parallel, particularly multiply and accumulate operations. General-purpose microprocessors can also be used as DSPs.

EEPROM: Electrically Erasable Programmable Read-Only Memory. This type of read-only memory can be programmed via software and erased electrically, rather than through an ultraviolet light source as EPROMs are. Flash memory is a recent form of EEPROM.

Endianness: The scheme that determines the order in which successive bytes of a data word are stored in memory. An aspect of the system’s memory mapping.

EFlash Memory: See EEPROM.

Exponent: Eight bits of a single-precision floating-point number or eleven bits of a double-precision floating-point number that follow a sign bit, indicating how the significand is to be scaled. Normally the exponent is biased so that the number is positive.

Fraction: The part of a floating-point number that is in the range [1.0, 2.0), represented in single-precision by 23 bits and in double-precision by 52 bits. Also known as the mantissa.

I2C: Inter-Integrated Circuit. This is a serial bus invented by Philips that allows low-speed peripherals to be attached to motherboards or embedded devices. Common applications of the bus include controlling LCD displays, reading real-time clocks, and accessing low-speed A/D converters.

Intellectual Property (IP): Legally, a term used to describe and protect artistic works, music, inventions, and other creations derived from human intellect. Semiconductor companies can license IP under contract from suppliers such as ARM, and are entitled to certain rights under the contract, e.g., the ability to produce products derived from the design they licensed.

Little-Endian: Byte ordering scheme in which bytes of increasing significance in a data word are stored at increasing addresses in memory.

Mantissa: See Fraction.

MB: Megabyte, or 1,048,576 bytes.

MMU: Memory Management Unit. A hardware option on a microprocessor that allows it to address more memory than physically present.

MPEG: Stands for Moving Picture Experts Group, but generally refers to the different standards for digitally encoding audio and video. Popular formats include MP3 for audio and MPEG-2 and MPEG-4 for video, which include standards for HDTV and high definition DVD players.

PROM: Programmable Read-Only Memory. A type of ROM that is programmed after the device has been built, using fuses that are changed just once.

RAM: Random Access Memory. This type of memory can be written to and read from. Forms of RAM include DRAM (Dynamic RAM) and SRAM (Static RAM).

RISC: Reduced Instruction Set Computer. A computer architecture having a small instruction set, where instructions are of a fixed length. Most RISC instructions execute in a single cycle, and data must be explicitly loaded and stored with separate instructions.

ROM: Read-Only Memory. This type of memory cannot be altered or programmed, and is usually configured at the time of manufacture.

Significand: In IEEE floating-point representations, the significand is the value 1.f, where f is the fraction.

SoC: System-on-Chip. This term refers to the integration of a processor core or cores, an internal bus, and peripherals on a single die to build a complete system.

Sticky bit: A bit that can only be cleared by explicitly writing a value of zero to it. In floating-point rounding operations, the sticky bit is a bit formed by ORing all bits with lower significance than the guard bit.

TCM: Tightly Coupled Memory. An area of low latency memory that provides predictable instruction execution or data load timing in cases where deterministic performance is required. TCMs are useful for holding important software routines, such as an interrupt handler, or data that is not well suited for caching. TCMs can be either ROM or RAM types.

UAL: Unified Assembly Language. With the introduction of Thumb-2 extensions, the syntax for instructions has been unified to allow the programmer to use a single mnemonic which can be ported to different architectures, especially for newer processors such as the Cortex family.

UART: Universal Asynchronous Receiver/Transmitter. This is a simple buffer which can be used to serially transmit and receive data. UARTs are commonly found on microcontrollers as memory-mapped peripherals.

USB: Universal Serial Bus. Largely a replacement for old serial and parallel connections on computers, the USB specification was developed by the USB Implementers Forum, which included companies such as HP, Apple, Microsoft, Intel, and NEC.

VPB: VLSI Peripheral Bus. A superset of ARM’s AMBA Peripheral Bus protocol defined by NXP.

Wafer: A thin, crystalline slice of material (usually silicon) used to make integrated circuits. Wafers are produced by slicing ingots of semiconducting material into thin plates and then polishing them.

Wi-Fi: The trade name for wireless networks based on the IEEE 802.11 standards.