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Encyclopedia > Motorola 68000

The Motorola 68000 is a 16/32-Bit [1] CISC microprocessor core designed and marketed by Freescale Semiconductor (formerly Motorola Semiconductor Products Sector). Introduced in 1979 as the first member of the successful 32-bit m68k family of microprocessors, it is generally software forward compatible with the rest of the line despite belonging to the 16-bit hardware technology generation. After twenty-seven years in production, the 68000 architecture, remains a popular choice for new designs. A complex instruction set computer (CISC) is a microprocessor instruction set architecture (ISA) in which each instruction can execute several low-level operations, such as a load from memory, an arithmetic operation, and a memory store, all in a single instruction. ... A microprocessor is a programmable digital electronic component that incorporates the functions of a central processing unit (CPU) on a single semiconducting integrated circuit (IC). ... Freescale sign Freescale Semiconductor, Inc. ... Motorola Inc. ... 32-bit is a term applied to processors, and computer architectures which manipulate the address and data in 32-bit chunks. ... The Motorola 680x0, 0x0, m68k, or 68k family of CISC microprocessor CPU chips were 32-bit from the start, and were the primary competition for the Intel x86 family of chips. ... Forward compatibility is the ability of a system to accept input from later versions of itself. ... In computer science, 16-bit is an adjective used to describe integers that are at most two bytes wide, or to describe CPU architectures based on registers, address buses, or data buses of that size. ... A typical vision of a computer architecture as a series of abstraction layers: hardware, firmware, assembler, kernel, operating system and applications (see also Tanenbaum 79). ... This article is about the engineering discipline. ...

Pre-release XC68000 chip manufactured in 1979.

Contents

Download high resolution version (1048x406, 128 KB)Motorola 68000 microprocessor pre-release version XC68000L with R9M mask, manufactured in December 1979. ... Download high resolution version (1048x406, 128 KB)Motorola 68000 microprocessor pre-release version XC68000L with R9M mask, manufactured in December 1979. ...

History

The 68000 grew out of the MACSS (Motorola Advanced Computer System on Silicon) project, begun in 1976 to develop an entirely new architecture without backward compatibility. It would be a higher-power sibling complementing the existing 8-bit 6800 line rather than a compatible successor. In the end, the 68000 did retain a bus protocol compatibility mode for existing 6800 peripheral devices, and a version with an 8-bit data bus was produced. However, the designers mainly focused on the future, or forward compatibility, which gave the M68K platform a head start against later 32-bit instruction set architectures. For instance, the CPU registers are 32 bits wide, though few self-contained structures in the processor itself operate on 32 bits at a time. The 68000 may be considered a 16-bit microprocessor which is microcoded to accelerate 32-bit tasks. The MACSS team drew heavily on the influence of minicomputer processor design, such as the PDP-11 and VAX systems, which were similarly microcoded. Year 1976 Pick up sticks(MCMLXXVI) was a leap year starting on Thursday (link will display full calendar) of the Gregorian calendar. ... This article or section does not cite its references or sources. ... Motorola 6800 Microprocessor The 6800 is a microprocessor produced by Motorola and released shortly after the Intel 8080 in 1975. ... For other senses of this word, see protocol. ... Forward compatibility (sometimes confused with extensibility) is the ability of a system to accept input intended for later versions of itself. ... In computing, a platform describes some sort of framework, either in hardware or software, which allows software to run. ... An instruction set, or instruction set architecture (ISA), describes the aspects of a computer architecture visible to a programmer, including the native datatypes, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O (if any). ... A microprogram is a program consisting of microcode that controls the different parts of a computers central processing unit (CPU). ... Minicomputer (colloquially, mini) is a largely obsolete term for a class of multi-user computers which make up the middle range of the computing spectrum, in between the largest multi-user systems (traditionally, mainframe computers) and the smallest single-user systems (microcomputers or personal computers). ... The PDP-11 was a 16-bit minicomputer sold by Digital Equipment Corp. ... VAX is a 32-bit computing architecture that supports an orthogonal instruction set (machine language) and virtual addressing (i. ...


In the mid 1970s, the 8-bit processor manufacturers raced to introduce the 16-bit generation. National Semiconductor had been first with its IMP-16 and PACE processors in 1973-1975, but these had issues with speed. The Intel 8086 in 1977 quickly gained popularity. The decision to leapfrog the competition and introduce a hybrid 16/32-bit design was necessary, and Motorola turned it into a coherent mission. Arriving late to the 16-bit arena afforded the new processor more integration (roughly 70000 transistors against the 29000 in the 8086), higher performance per clock, and acclaimed general ease of use. The 1970s decade refers to the years from 1970 to 1979, also called The Seventies. ... Categories: Electronics companies of the United States | Companies based in California | Corporation stubs ... The IMP-16C, by National Semiconductor, was the the first multi-chip 16-bit microprocessor. ... The 8086[1] is a 16-bit microprocessor chip designed by Intel in 1978, which gave rise to the x86 architecture. ... It has been suggested that this article or section be merged with Cycles Per Instruction. ...


The original MC68000 was fabricated using an HMOS process with a 3.5-micron feature size. Initial engineering samples were released in late 1979. Production chips were available in 1980, with initial speed grades of 4, 6, and 8 MHz. 10 MHz chips became available during 1981, and 12.5 MHz chips during 1982. The 16.67 MHz "12F" version of the MC68000, the fastest version of the original HMOS chip, was not produced until the late 1980s. NASAs Glenn Research Center cleanroom. ... HMOS, high-performance n-channel MOS, uses n-type metal-oxide-semiconductor field effect transistors (MOSFETs) to implement logic gates and other digital circuits. ... A micrometre (American spelling: micrometer, symbol µm) is an SI unit of length equal to one millionth of a metre, or about a tenth of the diameter of a droplet of mist or fog. ... Also: 1979 by Smashing Pumpkins. ... Year 1980 (MCMLXXX) was a leap year starting on Tuesday (link displays the 1980 Gregorian calendar). ... MegaHertz (MHz) is the name given to one million (106) Hertz, a measure of frequency. ... Year 1981 (MCMLXXXI) was a common year starting on Thursday (link displays the 1981 Gregorian calendar). ... Year 1982 (MCMLXXXII) was a common year starting on Friday (link displays the 1982 Gregorian calendar). ...


The 68000 had many high-end design wins early on. It became the dominant CPU for Unix based workstations, found its way into heralded computers such as the Amiga, Atari ST and Macintosh, and was used in the first generation of desktop laser printers. In 1982, the 68000 received an update to its ISA allowing it to support virtual memory by conforming to the Popek and Goldberg virtualization requirements. The updated chip was called the 68010. A further extended version which exposed 31 bits of the address bus was also produced, in small quantities, as the 68012. 1993 Apple LaserWriter Pro 630 laser printer A laser printer is a common type of computer printer that rapidly produces high quality text and graphics on plain paper. ... How virtual memory maps to physical memory Virtual memory is an addressing scheme implemented in hardware and software that allows non-contiguous memory to be addressed as if it were contiguous. ... The Popek and Goldberg virtualization requirements are a set of sufficient conditions for a computer architecture to efficiently support system virtualization. ... The Motorola MC68010 processor is a 16/32-bit microprocessor from Motorola, made in the early 1980s. ... The Motorola MC68012 processor is a 16/32-bit microprocessor from the early 1980s. ...


To support lower-cost systems and control applications with smaller memory sizes, Motorola introduced the 8-bit compatible MC68008, also in 1982. This was a 68000 with an 8-bit data bus and a smaller (20 bit) address bus. After 1982, Motorola devoted more attention to the 68020 and 88000 projects. The Motorola MC68008 is a 8/16/32-bit microprocessor from the early 1980s. ... The Motorola 68020 is a microprocessor from Motorola. ... The 88000 (m88k for short) is a microprocessor design produced by Motorola. ...


Other manufacturers

The 68HC000, the CMOS version of the 68000, was designed by Hitachi and jointly introduced in 1985.[2] Motorola's version was called the MC68HC000, while Hitachi's was the HD68HC000. The 68HC000 was eventually offered at speeds from 8 MHz to 20 MHz. Except for using CMOS circuitry, it behaved identically to the HMOS MC68000, but the change to CMOS greatly reduced its power consumption. The original HMOS MC68000 consumed around 1.35 watts at an ambient temperature of 25 °C, regardless of clock speed, while the MC68HC000 consumed only 0.13 watts at 8 MHz and 0.38 watts at 20 MHz. (Unlike CMOS circuits, HMOS still draws power when idle, so power consumption varies little with clock rate.) Motorola replaced the MC68008 with the MC68HC001 in 1990.[3] This chip resembled the 68HC000 in most respects, but its data bus could operate in either 16-bit or 8-bit mode, depending on the value of an input pin at reset. Thus, like the 68008, it could be used in systems with cheaper 8-bit memories. For other uses, see CMOS (disambiguation). ... For other uses, see Watt (disambiguation). ... Celsius is, or relates to, the Celsius temperature scale (previously known as the centigrade scale). ...


Several other companies were second-source manufacturers of the HMOS 68000. These included Hitachi (HD68000), Mostek (MK68000), Rockwell (R68000), Signetics (SCN68000), Thomson/SGS-Thomson (originally EF68000 and later TS68000), and Toshiba (TMP68000). Toshiba was also a second-source maker of the CMOS 68HC000 (TMP68HC000). In the electronics industry, a second source is a company that is licensed to manufacture and sell components originally designed by another company (the first source). ... Mostek was an integrated circuit manufacturer, founded in 1969 by ex-employees of Texas Instruments. ... Rockwell International was the ultimate incarnation of a series of companies under the sphere of influence of Willard Rockwell, who had made his fortune after the invention and successful launch of a new bearing system for truck axles in 1919. ... Signetics, once a major player in semiconductor manufacturing, made a variety of devices which included integrated circuits, bipolar and MOS, the Dolby circuit, logic, memory and analog circuits and Motorola clone CPUs, some of which were included in the first Atari video games. ... Thomson-CSF was a major electronics and defense contractor. ... STMicroelectronics is an international leading supplier of semiconductors. ... Toshiba Corporations headquarters (Center) in Hamamatsucho, Tokyo Toshiba Corporation sales by division for year ending March 31, 2005 Toshiba Corporation ) (TYO: 6502 ) is a Japanese multinational conglomerate manufacturing company, headquartered in Tokyo, Japan. ...


As a microcontroller core

After being succeeded by "true" 32-bit microprocessors, the 68000 was used as the core of many microcontrollers. In 1989, Motorola introduced the MC68302 communications processor,[4]. In 1991 Motorola introduced a separate processor chip based on this core, the MC68EC000.[5] In 1996 Motorola introduced this static core as a separate processor, the MC68SEC000.[6] It has been suggested that this article or section be merged with embedded microprocessor. ... Motorola 68EC000 controller The 68EC000 is a microprocessor from Motorola. ...


Motorola ceased production of the HMOS MC68000 and MC68008 in 1996,[7] but its spin-off company, Freescale Semiconductor, is still producing the MC68HC000, MC68HC001, MC68EC000, and MC68SEC000, as well as the MC68302 and MC68306 microcontrollers and later versions of the DragonBall family. The 68000's architectural descendants, the 680x0, CPU32, and Coldfire families, are also still in production. Year 1996 (MCMXCVI) was a leap year starting on Monday (link will display full 1996 Gregorian calendar). ... Freescale sign Freescale Semiconductor, Inc. ...


Applications

The 68000 was first used during the early 1980s in high-priced systems, including multiuser microcomputers like the WICAT 150 [1], Tandy TRS-80 Model 16, and Fortune 32:16; single-user workstations such as Hewlett-Packard's HP 9000 Series 200 systems, the first Apollo/Domain systems, Sun Microsystems' Sun-1, and the Corvus Concept; and graphics terminals like Digital Equipment Corporation's VAXstation 100 and Silicon Graphics' IRIS 1000 and 1200. While Unix systems soon abandoned the original 68000 due to limitations of the processor, its derivatives remained popular in the Unix market throughout the 1980s. Image File history File links Metadata Size of this preview: 800 × 450 pixelsFull resolution (2816 × 1584 pixel, file size: 954 KB, MIME type: image/jpeg) The name of this media object is misspelled, incomplete, misleading, cryptic, or does not conform to an established naming convention. ... Image File history File links Metadata Size of this preview: 800 × 450 pixelsFull resolution (2816 × 1584 pixel, file size: 954 KB, MIME type: image/jpeg) The name of this media object is misspelled, incomplete, misleading, cryptic, or does not conform to an established naming convention. ... The Commodore 64 was one of the most popular microcomputers of its era, and is the best selling model of home computer of all time. ... Tandy Corporation is the former name of the parent company of RadioShack Corporation, a Fort Worth, Texas-based company best known for its RadioShack electronics stores. ... This article does not cite any references or sources. ... Sun SPARCstation 1+, 25 MHz RISC processor from early 1990s A workstation, such as a Unix workstation, RISC workstation or engineering workstation, is a high-end desktop or deskside microcomputer designed for technical applications. ... The Hewlett-Packard Company (NYSE: HPQ), commonly known as HP, is a very large, global company headquartered in Palo Alto, California, United States. ... HP 9000 is the name for a line of computer systems produced by the Hewlett-Packard (HP) company. ... Apollo/Domain was a range of workstations developed and produced by Apollo Computers, Inc. ... Sun Microsystems, Inc. ... The name Sun-1 refers to the first generation of UNIX computer workstations and servers produced by Sun Microsystems, launched in 1982. ... Corvus Systems was a technology company founded by Michael DAddio and Mark Hahn in 1979 and located in San Jose, Silicon Valley in the U.S.. Corvus was a pioneer when personal computers (PCs) were still considered home computers. ... A computer terminal is an electronic or electromechanical hardware device that is used for entering data into, and displaying data from, a computer or a computing system. ... The DEC logo Digital Equipment Corporation was a pioneering American company in the computer industry. ... Silicon Graphics, Inc. ... Filiation of Unix and Unix-like systems Unix (officially trademarked as UNIX®, sometimes also written as or ® with small caps) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy. ...


During the mid 1980s, the 68000 was first used in personal and home computers, starting with the Apple Lisa and Macintosh, and followed by the Commodore Amiga, Atari ST, and Sharp X68000. The 68008, on the other hand, was only used in one home computer system, the Sinclair QL (though the QL was a sister machine to the ICL One Per Desk, which also used a 68008). A personal computer (PC) is a computer whose price, size, and capabilities make it useful for individuals. ... Children playing on a Amstrad CPC 464 in the 1980s. ... Apple Inc. ... The Apple Lisa was a revolutionary personal computer designed at Apple Computer during the early 1980s. ... For other uses, see Macintosh (disambiguation) and Mac. ... Commodore, the commonly used name for Commodore International, was an American electronics company based in West Chester, Pennsylvania which was a vital player in the home/personal computer field in the 1980s. ... This article is about the family of home computers. ... This article is about a corporate game company. ... The Atari ST is a home/personal computer that was commercially popular from 1985 to the early 1990s. ... Sharp Corporation ) (TYO: 6753 , LuxSE: SRP) is a Japanese electronics manufacturer, founded in 1912. ... The Sharp X68000, often referred to as the X68k, was a home computer released only in Japan by the Sharp Corporation. ... The Sinclair QL (for Quantum Leap), was a personal computer launched by Sinclair Research in 1984, as the successor to the ZX Spectrum. ...


The 68000 eventually saw its greatest success as a controller. As early as 1981, laser printers such as the Imagen Imprint-10 were driven by external controllers using the 68000 as the CPU. The first HP LaserJet, introduced in 1984, used an 8 MHz 68000 in its built-in controller. Similar 68000-based integrated controllers were subsequently used in many other laser printers, including the Apple LaserWriter, the first PostScript laser printer, introduced in 1985. The 68000 continued to be widely used in laser printers throughout the rest of the 1980s, persisting well into the 1990s in low-end printers. 1993 Apple LaserWriter Pro 630 laser printer A laser printer is a common type of computer printer that rapidly produces high quality text and graphics on plain paper. ... Imagén is a Puerto Rican fashion magazine. ... Image:1984 HP Laserjet. ... The Apple LaserWriter was one of the first laser printers available to the mass market. ... For the literary term, see Postscript. ...


Outside traditional commercial or domestic computing applications, the 68000 also saw success in the field of industrial control systems. Among the systems which benefited from having a 68000 or derivative as their microprocessor were families of Programmable Logic Controllers (PLCs) manufactured by Allen-Bradley, Texas Instruments and subsequently, following the acquisition of that division of TI, by Siemens. Users of such systems do not accept product obsolescence at the same rate as domestic users and it is entirely likely that despite having been installed over 20 years ago, many 68000-based controllers will continue in reliable service well into the 21st century. PLC & input/output arrangements A programmable logic controller (PLC), or programmable controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. ... A Milwaukee-based company that specializes in industrial control and automation products. ... Texas Instruments (NYSE: TXN), better known in the electronics industry (and popularly) as TI, is an American company based in Dallas, Texas, USA, renowned for developing and commercializing semiconductor and computer technology. ... Siemens redirects here. ...


As technological advances obsoleted the 68000 from use in the standalone computing market, its use grew in consumer and embedded applications. Video game manufacturers used the 68000 as the backbone of many arcade games and home game consoles. Atari's Food Fight, from 1983, was one of the first 68000-based arcade games. The 68000 was the main CPU of many arcade systems during the late 1980s and early 1990s, such as Sega's System 16, Capcom's CPS-1 and CPS-2, and SNK's Neo Geo. A number of arcade systems used two 68000s; some even used three. During the 1990s, as arcade systems switched to more powerful processors for the main CPU, they often continued to use the 68000 as a sound controller. “Computer and video games” redirects here. ... Centipede by Atari is a typical example of a 1980s era arcade game. ... “Game console” redirects here. ... A food fight is a spontaneous form of chaotic collective behavior, in which food is thrown around a room, usually a cafeteria, in the manner of projectiles. ... An arcade system board is a standardized printed circuit board or group of printed circuit boards that are used as the basis for multiple arcade games with very similar hardware requirements. ... This article is about the video game company. ... The Sega System 16 is an arcade system board released by Sega in 1985. ... For the original NASA meaning, see capsule communicator. ... The CPS-1 (CPシステム shīpī shisutemu) or Capcom Play System 1, is an arcade system board by Capcom that debuted in 1988 with Forgotten Worlds and Ghouls n Ghosts. ... CPS-2 (CPシステムII shīpī shisutemu tsū) or Capcom Play System 2, is an arcade system board that debuted in 1993 with Super Street Fighter 2, and Dungeons & Dragons: Tower of Doom. ... “SNK” redirects here. ... Neo-Geo is the name of a cartridge-based arcade and home video game system released in 1990 by Japanese game company SNK. The system offered comparatively colorful 2D graphics and high-quality sound. ...


The 68000 was also the central processor in several home game consoles of the late 1980s/early 1990s, including the Sega Mega Drive (Sega Genesis), the Sega Mega-CD (Sega CD), and the console version of the Neo Geo. Some later game consoles still included the 68000: the Sega Saturn used it as a dedicated sound controller, and in the Atari Jaguar it co-ordinated the activities of the other specialized graphics and sound chips. The Sega Mega Drive ) is a video game console released by Sega in Japan in 1988, North America in 1989, and the PAL region in 1990. ... This article or section does not cite its references or sources. ... Neo-Geo is the name of a cartridge-based arcade and home video game system released in 1990 by Japanese game company SNK. The system offered comparatively colorful 2D graphics and high-quality sound. ... It has been suggested that Arcade Racer Joystick be merged into this article or section. ... The Atari Jaguar is a video game console that was released in November 1993 to rival the Mega Drive/Genesis and the Super Nintendo Entertainment System as a powerful next generation platform. ...


The 68000-based 683XX microcontrollers have been utilized in a wide variety of applications, including networking and telephone equipment, television set-top boxes, and laboratory and medical instruments, among others. The MC68302 and its derivatives have been used in many communication products from Cisco, 3com, Ascend, Marconi and others. The DragonBall family was used in Palm Computing's popular Palm PDAs and in the Handspring Visor series, until Palm gradually phased out the architecture in favor of ARM processors. AlphaSmart uses the DragonBall family in later versions of its portable word processors. Categories: Corporation stubs | Electronics companies of the United States | Defunct computer companies of the United States ... Palm devices are Personal Digital Assistants (PDAs) which run Palm OS. This page describes the range of Palm devices, from the first generation of Palm machines known as the Pilot through to the latest models currently produced by Palm, Inc. ... A handspring is a gymnastic feat where the gymnast leaps forward from a standing position into a handstand and then onto his feet. ... The ARM architecture (previously, the Advanced RISC Machine, and prior to that Acorn RISC Machine) is a 32-bit RISC processor architecture developed by ARM Limited that is widely used in a number of embedded designs. ... The AlphaSmart is a brand of portable, battery powered, word-processing keyboards manufactured by AlphaSmart, Inc. ...


Texas Instruments uses the 68000 in its high-end graphing calculators, the TI-89 and TI-92 series and Voyage 200. Early versions of these used a specialized microcontroller with a static 68EC000 core; later versions use a standard MC68SEC000 processor. Texas Instruments (NYSE: TXN), better known in the electronics industry (and popularly) as TI, is an American company based in Dallas, Texas, USA, renowned for developing and commercializing semiconductor and computer technology. ... The TI-89 and the TI-89 Titanium are graphing calculators developed by Texas Instruments. ... The Texas Instruments TI-92 calculator, originally released in 1995, was a large calculator with a QWERTY keyboard. ...


Architecture

Address bus

The 68000 implements a 24-bit address bus, allowing it to address up to 16 MB of physical memory. Address storage and computation used 32 bits, however, with the high-order byte ignored due to the physical lack of pins. This allowed it to run software written for a flat 32-bit address space. By modern definition this meant that the 68000 was a 32-bit microprocessor. Motorola's intent with the internal 32-bit address space was forwards compatibility, making it feasible to write 68000 software that would take full advantage of later 32-bit implementations of the 68000 instruction set. Contrast this with the problems posed by segmented architectures such as the 80286 which eventually had to be emulated entirely in software. It is seen as an act of great foresight for the 68000 series to have been 32-bit from the beginning. In computing, an address space defines a range of discrete addresses, each of which may correspond to a physical or virtual memory register, a network host, peripheral device, disk sector or other logical or physical entity. ...


However, this did not prevent programmers from writing forward incompatible software. "24-bit" software that discarded the upper address byte, or used it for purposes other than addressing, could fail on 32-bit 68K implementations.


Internal registers

The CPU had eight 32-bit general-purpose data registers (D0-D7), and eight address registers (A0-A7). The last address register was also the standard stack pointer, and could be called either A7 or SP. This was a good number of registers in many ways. It was small enough to allow the 68000 to respond quickly to interrupts (because only 15 or 16 had to be saved), and yet large enough to make most calculations fast. “CPU” redirects here. ... In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to frequently used values—typically, these values are involved in multiple expression evaluations occurring within a small region on the program. ... Simple representation of a stack In computer science, a stack is a temporary abstract data type and data structure based on the principle of Last In First Out (LIFO). ... In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ...


Having two types of registers was mildly annoying at times, but not hard to use in practice. Reportedly, it allowed the CPU designers to achieve a higher degree of parallelism, by using an auxiliary execution unit for the address registers. In computer engineering, an execution unit is a part of a CPU that performs the operations and calculations called for by the program. ...


Integer representation in the 68000 family is big-endian. In computing, endianness is the byte (and sometimes bit) ordering in memory used to represent some kind of data. ...


Status register

The 68000 comparison, arithmetic and logic operations set bits in a status register to record their results for use by later conditional jumps. The bits were "Z"ero, "C"arry, o"V"erflow, e"X"tend, and "N"egative. The e"X"tend bit deserves special mention, because it was separated from the Carry. This permitted the extra bit from arithmetic, logic and shift operations to be separated from the carry for flow-of-control and linkage.


The instruction set

The designers attempted to make the assembly language orthogonal. That is, instructions were divided into operations and address modes, and almost all address modes were available for almost all instructions. Many programmers disliked the "near" orthogonality, while others were grateful for the attempt. Orthogonal instruction set is a term used in computer science. ... Addressing modes, a concept from computer science, are an aspect of the instruction set architecture in most central processing unit (CPU) designs. ...


At the bit level, the person writing the assembler would clearly see that these "instructions" could become any of several different op-codes. It was quite a good compromise because it gave almost the same convenience as a truly orthogonal machine, and yet also gave the CPU designers freedom to fill in the op-code table. See the terminology section, below, regarding inconsistent use of the terms assembly and assembler. ...


With only 56 instructions the minimal instruction size was huge for its day at 16 bits. Furthermore, many instructions and addressing modes added extra words on the back for addresses, more address-mode bits, etc.


Many designers believed that the MC68000 architecture had compact code for its cost, especially when produced by compilers. This belief in more compact code led to many of its design wins, and much of its longevity as an architecture.


This belief (or feature, depending on the designer) continued to make design wins for the instruction set (with updated CPUs) up until the ARM architecture introduced the Thumb instruction set that was similarly compact. The ARM architecture (previously, the Advanced RISC Machine, and prior to that Acorn RISC Machine) is a 32-bit RISC processor architecture developed by ARM Limited that is widely used in a number of embedded designs. ...


Privilege levels

The CPU, and later the whole family, implemented exactly two levels of privilege. User mode gave access to everything except the interrupt level control. Supervisor privilege gave access to everything. An interrupt always became supervisory. The supervisor bit was stored in the status register, and visible to user programs.


A real advantage of this system was that the supervisor level had a separate stack pointer. This permitted a multitasking system to use very small stacks for tasks, because the designers did not have to allocate the memory required to hold the stack frames of a maximum stack-up of interrupts. In computing, multitasking is a method by which multiple tasks, also known as processes, share common processing resources such as a CPU. In the case of a computer with a single CPU, only one task is said to be running at any point in time, meaning that the CPU is...


Interrupts

The CPU recognized 7 interrupt levels. Levels 1 through 7 were strictly prioritized. That is, a higher-numbered interrupt could always interrupt a lower-numbered interrupt. In the status register, a privileged instruction allowed one to set the current minimum interrupt level, blocking lower priority interrupts. Level 7 was not maskable - in other words, an NMI. Level 1 could be interrupted by any higher level. Level 0 means no interrupt. The level was stored in the status register, and was visible to user-level programs. In computing, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ... A Non-Maskable Interrupt (NMI) is a special type of interrupt that can not be ignored by standard interrupt masking techniques. ...


Hardware interrupts are signalled to the CPU using three inputs that encode the highest pending interrupt priority. A separate interrupt controller is usually required to encode the interrupts, though for systems that do not require more than three hardware interrupts it is possible to connect the interrupt signals directly to the encoded inputs at the cost of additional software complexity. The interrupt controller can be as simple as a 74LS148 priority encoder, or may be part of a VLSI peripheral chip such as the MC68901 Multi-Function Peripheral, which also provided a UART, timer, and parallel I/O. The 7400 chip, containing four NANDs. ... A UART or universal asynchronous receiver-transmitter is a piece of computer hardware that translates between parallel bits of data and serial bits. ...


The "exception table" (interrupt vector addresses) was fixed at addresses 0 through 1023, permitting 256 32-bit vectors. The first vector was the starting stack address, and the second was the starting code address. Vectors 3 through 15 were used to report various errors: bus error, address error, illegal instruction, zero division, CHK & CHK2 vector, privilege violation, and some reserved vectors that became line 1010 emulator, line 1111 emulator, and hardware breakpoint. Vector 24 started the real interrupts: spurious interrupt (no hardware acknowledgement), and level 1 through level 7 autovectors, then the 15 TRAP vectors, then some more reserved vectors, then the user defined vectors.


Since at a minimum the starting code address vector must always be valid on reset, systems commonly included some nonvolatile memory (e.g. ROM) starting at address zero to contain the vectors and bootstrap code. However, for a general purpose system it is desirable for the operating system to be able to change the vectors at runtime. This was often accomplished by either pointing the vectors in ROM to a jump table in RAM, or through use of bank-switching to allow the ROM to be replaced by RAM at runtime. Read-only memory (usually known by its acronym, ROM) is a class of storage media used in computers and other electronic devices. ... In computing, booting (booting up) is a bootstrapping process that starts operating systems when the user turns on a computer system. ... RAM redirects here. ...


The 68000 did not meet the Popek and Goldberg virtualization requirements for full processor virtualization because it had a single unprivileged instruction "MOVE from SR", which allowed user-mode software read-only access to a small amount of privileged state. The Popek and Goldberg virtualization requirements are a set of sufficient conditions for a computer architecture to efficiently support system virtualization. ...


The 68000 was also unable to easily support virtual memory, which requires the ability to trap and recover from a failed memory access. The 68000 does provide a bus error exception which can be used to trap, but it does not save enough processor state to resume the faulted instruction once the operating system has handled the exception. Several companies did succeed in making 68000 based Unix workstations with virtual memory that worked, by using two 68000 chips running in parallel on different phased clocks. When the "leading" 68000 encountered a bad memory access, extra hardware would interrupt the "main" 68000 to prevent it from also encountering the bad memory access. This interrupt routine would handle the virtual memory functions and restart the "leading" 68000 in the correct state to continue properly synchronized operation when the "main" 68000 returned from the interrupt. How virtual memory maps to physical memory Virtual memory is an addressing scheme implemented in hardware and software that allows non-contiguous memory to be addressed as if it were contiguous. ...


These problems were fixed in the next major revision of the 68K architecture, with the release of the MC68010. The Bus Error and Address Error exceptions pushed a large amount of internal state onto the supervisor stack in order to facilitate recovery, and the MOVE from SR instruction was made privileged. A new unprivileged "MOVE from CCR" instruction was provided for use in its place by user mode software; an operating system could trap and emulate user-mode MOVE from SR instructions if desired.


Instruction set details

The standard addressing modes are: Addressing modes, a concept from computer science, are an aspect of the instruction set architecture in most central processing unit (CPU) designs. ...

  • Register direct
    • data register, e.g. "D0"
    • address register, e.g. "A6"
  • Register indirect
    • Simple address, e.g. (A0)
    • Address with post-increment, e.g. (A0)+
    • Address with pre-decrement, e.g. -(A0)
    • Address with a 16-bit signed offset, e.g. 16(A0)
    • Note that the actual increment or decrement size was dependent on the operand request: a byte read instruction incremented the address register by 1, a word read by 2, and a long read by 4.
  • Register indirect with an Index
    • 8-bit signed offset, e.g. 8(A0, D0) or 8(A0, A1)
  • PC (program counter) relative with displacement
    • 16-bit signed offset, e.g. 16(PC). This mode was very useful.
    • 8-bit signed offset with index, e.g. 8(PC, D2)
  • Absolute memory location
    • Either a number, e.g. "$4000", or a symbolic name translated by the assembler
    • Most 68000 assemblers used the "$" symbol for hexadecimal, instead of "0x".
  • Immediate mode
    • Stored in the instruction, e.g. "#400".

Plus: access to the status register, and, in later models, other special registers. In mathematics and computer science, hexadecimal, base-16, or simply hex, is a numeral system with a radix, or base, of 16, usually written using the symbols 0–9 and A–F, or a–f. ... A status register is a collection of flag bits for a microprocessor that indicates the status of various mathematical operations. ...


Most instructions had dot-letter suffixes, permitting operations to occur on 8-bit bytes (".b"), 16-bit words (".w"), and 32-bit longs (".l").


Most instructions are dyadic, that is, the operation has a source, and a destination, and the destination is changed. Notable instructions were: Dyadic Dyadic tensor Dyadic fraction Dyadic counterpoint, the voice-against-voice conception of polyphony Dyad This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

  • Arithmetic: ADD, SUB, MULU (unsigned multiply), MULS (signed multiply), DIVU, DIVS, NEG (additive negation), and CMP (a sort of subtract that set the status bits, but did not store the result)
  • Logic: EOR (exclusive or), AND, NOT (logical not)
  • Shifting: (logical, i.e. right shifts put zero in the most significant bit) LSL, LSR, (arithmetic shifts, i.e. sign-extend the most significant bit) ASR, ASL, (Rotates through eXtend and not:) ROXL, ROXR, ROL, ROR
  • Bit manipulation in memory: BSET (to 1), BCLR (to 0), and BTST (set the Zero bit)
  • Multiprocessing control: TAS, test-and-set, performed an indivisible bus operation, permitting semaphores to be used to synchronize several processors sharing a single memory
  • Flow of control: JMP (jump), JSR (jump to subroutine), BSR (relative address jump to subroutine), RTS (return from subroutine), RTE (return from exception, i.e. an interrupt), TRAP (trigger a software exception similar to software interrupt), CHK (a conditional software exception)
  • Branch: Bcc (a branch where the "cc" specified one of 16 tests of the condition codes in the status register: equal, greater than, less-than, carry, and most combinations and logical inversions, available from the status register).
  • Decrement-and-branch: DBcc (where "cc" was as for the branch instructions) which decremented a D-register and branched to a destination provided the condition was still true and the register had not been decremented to -1. This use of -1 instead of 0 as the terminating value allowed the easy coding of loops which had to do nothing if the count was 0 to begin with, without the need for an additional check before entering the loop.

Binary-coded decimal (BCD) is a numeral system used in computing and in electronics systems. ... In telecommunication, an arithmetic shift is a shift, applied to the representation of a number in a fixed radix numeration system and in a fixed-point representation system, and in which only the characters representing the fixed-point part of the number are moved. ... Bit manipulation is the act of algorithmically manipulating bits or other pieces of data shorter than byte. ... Multiprocessing is traditionally known as the use of multiple concurrent processes in a system as opposed to a single process at any one instant. ... In computer science, the test-and-set instruction is an instruction used to atomically write to a memory location. ... This article is about the computer science application of mutual exclusion. ... In computer science, a subroutine (function, method, procedure, or subprogram) is a portion of code within a larger program, which performs a specific task and can be relatively independent of the remaining code. ... Exception may refer to: An action that is not part of normal operations or standards. ...

Notes

  1. ^ Motorola Literature Distribution, Phonenix, AZ (1992). M68000 Family Programmer's Reference Manual. [Motorola], pg 1-1. ISBN 013-723289-6. 
  2. ^ "Company Briefs", The New York Times, September 21, 1985, available from TimesSelect (subscription).
  3. ^ "68HC001 obsoletes 68008.", Microprocessor Report, June 20, 1990; available from HighBeam Research (subscription).
  4. ^ "Multiprotocol processor marries 68000 and RISC.", ESD: The Electronic System Design Magazine, November 1, 1989; available from AccessMyLibrary.
  5. ^ "Motorola streamlines 68000 family; "EC" versions of 68000, '020, '030, and '040, plus low-end 68300 chip.", Microprocessor Report, April 17, 1991; available from HighBeam Research (subscription).
  6. ^ "Motorola reveals MC68SEC000 processor for low power embedded applications", Motorola press release, November 18, 1996; archived by Internet Archive on March 28, 1997.
  7. ^ comp.sys.m68k Usenet posting, May 16, 1995; also see other posts in thread. The end-of-life announcement was in late 1994; according to standard Motorola end-of-life practice, final orders would have been in 1995, with final shipments in 1996.

is the 264th day of the year (265th in leap years) in the Gregorian calendar. ... This article is about the year. ... is the 171st day of the year (172nd in leap years) in the Gregorian calendar. ... Year 1990 (MCMXC) was a common year starting on Monday (link displays the 1990 Gregorian calendar). ... is the 305th day of the year (306th in leap years) in the Gregorian calendar. ... Year 1989 (MCMLXXXIX) was a common year starting on Sunday (link displays 1989 Gregorian calendar). ... is the 107th day of the year (108th in leap years) in the Gregorian calendar. ... Year 1991 (MCMXCI) was a common year starting on Tuesday (link will display the 1991 Gregorian calendar). ... is the 322nd day of the year (323rd in leap years) in the Gregorian calendar. ... Year 1996 (MCMXCVI) was a leap year starting on Monday (link will display full 1996 Gregorian calendar). ... is the 87th day of the year (88th in leap years) in the Gregorian calendar. ... For the band, see 1997 (band). ... is the 136th day of the year (137th in leap years) in the Gregorian calendar. ... Year 1995 (MCMXCV) was a common year starting on Sunday (link will display full 1995 Gregorian calendar). ...

See also

The Motorola 680x0/0x0/m68k/68k/68K family of CISC microprocessor CPU chips were 32-bit from the start, and were the primary competition for the Intel x86 family of chips in personal computers of the 1980s and early 1990s. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... MacsBug is a low-level debugger for the Motorola 68000 family of processors specifically for the Apple Macintosh. ... The Zilog Z80 is an 8-bit microprocessor designed and manufactured by Zilog from 1976 onwards. ...

References

External links


  Results from FactBites:
 
Motorola 68000 microprocessor family (283 words)
Motorola 68000 (MC68000) is the first member of 680x0 line of microprocessors.
Motorola also made 68008 - a version of 68000 CPU with 8-bit external data bus.
The 68000 architecture was much more flexible than other CPU families (z80, 80x86, z80000, etc) from programming point of view as it could be easily expanded to support full 32-bit data and address buses.
PDA Encyclopedia - Motorola 68000 (1984 words)
The Motorola 68000 is a CISC microprocessor, the first member of a successful family of microprocessors, which were all mostly software compatible.
In the Sega Saturn, the 68000 was used as the sound processor, and in the Atari Jaguar they were used as a main controller for all the other dedicated hardware IC's.
The 68000 was also unable to correctly return from an exception on a failing memory access, a crucial feature to enable true virtual memory.
  More results at FactBites »

 
 

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