Microprocessor Dictionary

accumulator-a register within the CPU. This register will be one of the operands in an arithmetic or logical operation.

address-a binary pattern used to select a location in memory. In this text, addresses are 16 bits wide.

addressing modes-techniques used by software or hardware in calculating an address.

ALU-arithmetic logic unit; the section of the CPU that performs calculations for arithmetic and logical operations.

assembler-a program that translates mnemonic code into machinelevel code.

asynchronous-an event or operation not controlled by the master clock.

base address-the location of the first datum in a data table.

bit-a binary digit.

BCD-binary coded decimal; a number system in which each group of 4 bits (referred to as decades) represents a single decimal digit.

breakpoint-a place in a program where execution is temporarily stopped. Once a breakpoint is reached, analysis of the program can be performed.

buffer-a circuit that can be used to isolate one part of the computer from another. Buffers often provide extra current capabilities not found in the circuit driving the inputs. A buffer can also be used as a temporary storage register.

bus-a set of lines used to move information from one part of the computer to another. Typically, a bus is divided into three functional groups: data, address, and control.

bus contention-two or more circuits trying to place information on a common line at the same time.

byte-a group of 8 bits.

CPU-central processing unit; a section of a computer responsible for execution of programs. This section manipulates the data, generates control signals, and stores results. In modern computers these functions have been integrated into a single IC. The 8080, 8085, and Z80 are examples of CPUs.

clock cycle-the basic unit of processor activity.

compiler-a program that translates highlevel code into machine code.

controller-a circuit that acts as an interface between the computer and a device such as a disk drive. The controller will pass information back and forth between the computer and the device and will generate specialized control signals needed to operate the device.

DAC-digitaltoanalog converter.

deviceselect pulse-a control pulse created by logically combining a port address with an IN or OUT control signal.

DMA-direct memory access; a process in which circuits other than the CPU can read from or write to memory without processor intervention.

displacement-the amount by which a location differs from a reference point. When using data tables, the reference point is usually the base address.

duplex-twoway data transfers. Half duplex is twoway communication, with each end of the system taking turns transmitting. Full duplex is twoway communication that occurs simultaneously.

dynamic memory-a memory in which information is stored capacitively. This type of memory requires periodic refresh to replenish capacitor charges.

EEPROM-electrically erasable programmable read only memory.

EPROM-erasable by ultraviolet light.

firmware-a software routine that has been stored in a read only memory and thus is available at power up without the need for reloading the code.

flag-a flipflop used to indicate the status of an operation. For example, the zero flag will indicate if an operation results in zero if it is set.

flowchart-a pictorial diagram of the logical sequence of a program.

handshaking-the exchange of control and status information between two circuits. Handshaking is used to coordinate the transfer of data between circuits.

hardware- the physical parts of a system.

highlevel language-a computer language such as FORTRAN or COBOL. Such languages are Englishlike, requiring a compiler to translate them into machine code.

ICE-in circuit emulator.

index register-a specialpurpose register used by a processor when performing indexed addressing. The value in the index register is usually the reference location to which a displacement will be added.

I/O-input/output; the process by which the computer communicates with the outside world.

instruction-a computer command.

instruction cycle-the time and activities associated with the performance of an instruction.

instruction fetch-a machine cycle used by the processor to obtain instructions from memory.

instruction register-the part of the CPU that stores the instruction while it is being decoded.

instruction set-the group of instructions that is recognized by a processor.

interrupt-an asynchronous request by a circuit asking for the processor's attention. If acknowledged, the processor will temporarily stop what it was doing and interact with the circuit that generated the interrupt.

interrupt service routine-a section of code written to handle the tasks associated with an interrupt request.

interrupt vector-a special code that identifies the circuit requesting an interrupt.

invisible subtraction-a subtraction in which the answer is not stored back in the accumulator. The results of the subtraction can, however, affect the flags, making it possible to make decisions based on the result.

isolated I/O-a method of I/O that differentiates between memory and I/O ports. In this text, the only register that can be used with isolated I/O is the accumulator.

linear decoding-a method of addressing a circuit using a single address line.

logical construct-a method of organizing how a task will be performed. When used in programming, constructs partition the code into sections in which each section has but one entry point and one exit point.

machine cycle-a set of clock states grouped together to perform a data transfer.

machine language-a computer language that is directly executable by a computer without the need for translation by a compiler or an assembler. Although the computer works on binary patterns, the program can usually be entered in octal or hexadecimal.

masking-a process in which an operation can be performed on a single bit.

memory cell-a circuit in memory that represents a single bit.

memory map-documentation that lists or shows the function of each location in memory.

memory mapped I/O-a system of I/O in which each I/O location is treated as if it were memory.

microprocessor-an integrated circuit in which CPU, ALU, and control functions are combined.

mnemonic-an Englishlike representation of an instruction.

monitor program-a program, usually stored in ROM, that is responsible for basic computer operations.

nesting-the technique of placing a loop or subroutine within another loop or subroutine.

nibble-4 bits.

nonmaskable interrupt-an interrupt that cannot be turned off.

operating system-a program similar to a monitor program, but more sophisticated. Not only does it handle basic computer functions, it is capable of interacting with peripherals such as disk drives and printers.

up code-a binary pattern that when loaded into the instruction register will cause the CPU to perform tasks associated with the instruction.

page-256 bytes of memory.

parallel-a bus system in which information is moved in multibit units simultaneously.

polling-a process in which the status of devices attached to a bus system is periodically sampled.

port-an interface circuit capable of receiving from or placing information on the bus.

priority-the level of importance of an event. Most often, interrupts are assigned priorities.

program counter-a 16bit register that places addresses on the bus to retrieve information stored within a program.

programmable interface chip-an IC in which the specific tasks to be performed are not hardwired into the chip, but selectable through the use of command words.

PROM-programmable read only memory.

random access-each location within memory can be directly accessed without the need to sequence through prior locations. Direct access is probably more appropriate, as this access method is not really random.

read-to transfer information into the CPU.

relative addressing-an addressing mode that calculates a new address based on the position of an instruction within a program.

sequential access-a method of access in which all prior records or locations must be traversed before reaching the desired location or record.

signature analysis-a troubleshooting technique in which a stream of serial data is converted into a binary pattern that can then be compared to a pattern known to represent a functional circuit.

simplex-oneway communication.

single step-a process in which a program can be performed one instruction or one machine cycle at a time.

stack-an area of memory used to implement a data structure that follows the last in, first out method of access. In most cases, the stack is used by the processor to keep track of subroutine calls and returns.

stack pointer-a specialpurpose register that tracks the location of the last entry in the stack.

static memory-memory in which the basic cell circuit consists of a flipflop.

synchronous-an event or operation that takes place in step with a master clock.

throughput-the amount of information processed in a given time.

USART-universal synchronous asynchronous receiver transmitter; a specialpurpose IC used in data communications.

volatile-memory in which data is lost when power is removed.

word-16 bits.

write-data transfer out of the CPU.

History of Microprocessors

1971 - November 15	First microprocessor, the 4004, developed by Marcian E. Hoff for Intel, was released. It contains the equivalent of 2300 transistors and was a 4 bit processor. It is capable of around 60,000 Interactions per second (0.06 MIPs), running at a clock rate of 108KHz.
1972 - April 1	8008 Processor released by Intel.
1974 - April 1	Introduction of 8080. An 8 Bit Microprocessor from Intel.
1976?	Introduction of 8085.
1976	Z80 released by Zilog, and the basis for the computer boom in the early 1980s. It was an 8 bit microprocessor. CP/M was written for the Z80 as well as software like Wordstar and dBase II - and it formed the basis for the Sinclair Spectrum of 1982.
1976	6502, 8 bit microprocessor developed and later chosen to equip the Apple II computer. Also fitted in the original Acorn machine, BBC Micro, Commodore 64 and Commodore PET.
1978 - June 8	Introduction of 8086 by Intel, the first commercially successful 16 bit processor. It was too expensive to implement in early computers, so an 8 bit version was developed (the 8088), which was chosen by IBM for the first IBM PC. This ensured the success of the x86 family of processors that succeeded the 8086 since they and their clones are used in every IBM PC compatible computer. The available clock frequencies are 4.77, 8 and 10 MHz. It has an instruction set of about 300 operations. At introduction the fastest processor was the 8 MHz version which achieved 0.8 MIPs and contained 29,000 transistors.
1979 - June 1	Introduction of 8088, a step down from the 8086 as it contains just an 8 bit data bus - but this makes it cheaper to implement in computers.
1979	The 68000 Microprocessor launched by Motorola. Used by Apple for the Macintosh and by Atari for the ST series. Later versions of the processor include the 68020 used in the Macintosh II.
1981	Introduction of 80186/80188. These are rarely used on PCs as they incorporate a built in DMA and timer chip - and thus have register addresses incompatible with other IBM PCs.
1982 - February 1	80286 Released. It supports clock frequencies of up to 20 MHz and implements a new mode of operation, protected mode - allowing access to more memory (up to 16 Mbytes compared to 1 MB for the 8086. The virtual address space can appear to be up to 1 GB through the use of virtual memory). It includes an extended instruction set to cope with this new mode of operation. At introduction the fastest version ran at 12.5 MHz, achieved 2.7 MIPs and contained 134,000 transistors.
1985 October 17	80386 DX released. It supports clock frequencies of up to 33 MHz and can address up to 4 GB of memory and virtual memory of up to 64 TERABYTES! It also includes a bigger instruction set than the 80286. At the date of release the fastest version ran at 20 MHz and achieved 6.0 MIPs. It contained 275,000 transistors.
1988 - June 16	80386 SX released as a cheaper alternative -to the 80386 DX. It had a narrower (16 bit) time multiplexed bus. This reduction in pins, and the easier integration with 16 bit devices made the cost savings.
1989 - April 10	80486 DX released by Intel. It contains the equivalent of about 1.2 million transistors. At the time of release the fastest version ran at 25 MHz and achieved up to 20 MIPs. Later versions, such as the DX/2 and DX/4 versions achieved internal clock rates of up to 100 MHz.
1991 - April 22	80486 SX released as cheaper alternative to 80486 DX - the key difference being the lack of an integrated F.P.U.
1993 - March 22	Intel Pentium released. At the time it was only available in 60 & 66 MHz versions which achieved up to 100 MIPs, with over 3.1 million transistors.
1994 - March 7	Intel Release the 90 & 100 MHz versions of the Pentium Processor.
1994 - October 10	Intel Release the 75 MHz version of the Pentium Processor.
1995 - March 27	Intel release the 120 MHz version of the Pentium processor.
1995 - June 1	Intel release the 133 MHz version of the Pentium processor.
1995 - November 1	Pentium Pro released. At introduction it achieved a clock speed of up to 200 MHz (there were also 150, 166 and 180 MHz variants released on the same date), but is basically the same as the Pentium in terms of instruction set and capabilities. It achieves 440 MIPs and contains 5.5 million transistors - this is nearly 2400 times as many as the first microprocessor, the 4004 - and capable of 70,000 times as many instructions per second.
1996 - January 4	Intel release the 150 & 166 MHz versions of the Pentium Processor. They contain the equivalent of over 3.3 million transistors.
1996 - October 6	Intel release the 200 Mhz version of the Pentium Processor.
1997 - January 8	Intel released Pentium MMX (originally 166 and 200 Mhz versions), for games and multimedia enhancement. To most people MMX is simply another 3-letter acronym and people wearing coloured suits on Intel ads, and to programmers in meant an even further expanded instruction set that provides, amongst other functions, enhanced 64-bit support - but software needs to be specially written to work with the new functions. A major rival clone, the AMD-K6-MMX containing a similar instruction set, caused a legal challenge from Intel on the right to use the trademarked name MMX - it was not upheld.
1997 - May 7	Intel Release their Pentium II processor (233, 266 and 300 Mhz versions). It featured, as well as an increased instruction set, a much larger on-chip cache.
1997 - June 2	Intel release the 233 MHz Pentium MMX.
1998 - February	Intel released of 333 MHz Pentium II processor. Code-named Deschutes these processors use the new 0.25 micron manufacturing process to run faster and generate less heat than before.
1999 - Feb 22	AMD release K6-III 400MHz version, 450 to OEMS. In some tests it outperforms soon-to-be released Intel P-III. It contains approximately 23 million transistors, and is based on 100Mhz super socket 7 motherboards, an improvement on the 66MHz buses their previous chips were based on. This helps its performance when compared to Intel's Pentium II - which also uses a 100MHz bus speed.
1999 - Nov 29	AMD release Athlon 750MHz version.
2000 - Jan 19	Transmeta launch their new 'Crusoe' chips. Designed for laptops these prvoide comparible performance to the mid-range Pentium II chips, but consume a tiny fraction of the power. They are a new and exciting competitor to Intel in the x86 market.
2000 - March 6	AMD Release the Athlon 1GHz.
2000 - March 8	Intel release very limited supplies of the 1GHz Pentium III chip.

Microprocessor: Definition

Microcomputer
The term microcomputer is used to describe a system that includes at minimum a microprocessor, program memory, data memory, and an input-output (I/O) device. Some microcomputer systems include additional components such as timers, counters, and analog-to-digital converters. Thus, a microcomputer system can be anything from a large computer having hard disks, floppy disks, and printers to a single-chip embedded controller.

Microcontroller
A microcontroller is a single-chip computer. Micro suggests that the device is small, and controller suggests that it is used in control applications. Another term for microcontroller is embedded controller, since most of the microcontrollers are built into (or embedded in) the devices they control.

Microcomputer Block Diagram:

Intel Microprocessors and their Details:

MICROPROCESSOR	YEAR	SPEED	WORD LENGTH	TRANSISTORS	MIPS
Intel 4004	1969	108 KHz	4-bit	2,300	.06
Intel 8008	1972	200 KHz	8-bit	3,500	.06
Intel 8080	1974	2 MHz	8-bit	6,000	.64
Intel 8086	1978	4.47 MHz	16-bit	29,000	.66
Intel 8088	1981	4.47 MHz	16-bit	29,000	.75
Intel 80286	1982	12 MHz	16-bit	134,000	2.66
Intel 80386	1985	16-33 MHz	32-bit	275,000	4
Intel 80486 (i486)	1989	20-100 MHz	32-bit	1.2 Million	70
Intel 80586 (Pentium)	1993	75-200 MHz	32-bit	3.3 Million	126 - 203
Intel Pentium Pro	1995	150-200 MHz	32-bit	5.5 Million	300
Intel Pentium MMX	1997	166-233 MHz	32-bit	4.5 Million	-
Intel Pentium II	1997	233-450 MHz	32-bit	7.5 Million	-
Intel Pentium III	1999	450-933 MHz	32-bit	Over 9.5 Million	-
Intel Itanium Processor (formerly Merced Processor)	2000	1 GHz	64-bit	15,000,000	1,200

Speed is measured in terms of Hz. 1 Hz=1 cycle per second (1 Particular Job per second)
In a single processors millions of transistors may be used.
MIPS: Millions of Instruction Per Second (The speed in terms of Instruction performed in a second)
The First Microprocessor was the 4-bit Intel 4004 Processor.