|General purpose||8× 32-bit + 7 address registers also usable for most operations + stack pointer|
The Motorola 68000 ("'sixty-eight-thousand'"; also called the m68k or Motorola 68k, "sixty-eight-kay") is a 16/32-bit CISC microprocessor, introduced in 1979 by Motorola Semiconductor Products Sector.
A complex instruction set computer is a computer in which single instructions can execute several low-level operations or are capable of multi-step operations or addressing modes within single instructions. The term was retroactively coined in contrast to reduced instruction set computer (RISC) and has therefore become something of an umbrella term for everything that is not RISC, from large and complex mainframe computers to simplistic microcontrollers where memory load and store operations are not separated from arithmetic instructions. A modern RISC processor can therefore be much more complex than, say, a modern microcontroller using a CISC-labeled instruction set, especially in the complexity of its electronic circuits, but also in the number of instructions or the complexity of their encoding patterns. The only typical differentiating characteristic is that most RISC designs use uniform instruction length for almost all instructions, and employ strictly separate load/store-instructions.
A microprocessor is a computer processor that incorporates the functions of a central processing unit on a single integrated circuit (IC), or at most a few integrated circuits. The microprocessor is a multipurpose, clock driven, register based, digital integrated circuit that accepts binary data as input, processes it according to instructions stored in its memory and provides results as output. Microprocessors contain both combinational logic and sequential digital logic. Microprocessors operate on numbers and symbols represented in the binary number system.
Motorola, Inc. was an American multinational telecommunications company founded on September 25, 1928, based in Schaumburg, Illinois. After having lost $4.3 billion from 2007 to 2009, the company was divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011. Motorola Solutions is generally considered to be the direct successor to Motorola, as the reorganization was structured with Motorola Mobility being spun off. Motorola Mobility was sold to Google in 2012, and acquired by Lenovo in 2014.
The design implements a 32-bit instruction set, with 32-bit registers and a 32-bit internal data bus. The address bus is 24-bits and does not use memory segmentation, which made it popular with programmers. Internally, it uses a 16-bit data ALU and two additional 16-bit ALUs used mostly for addresses,and has a 16-bit external data bus. For this reason, Motorola referred to it as a 16/32-bit processor.
In computer architecture, 32-bit integers, memory addresses, or other data units are those that are 32 bits wide. Also, 32-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. 32-bit microcomputers are computers in which 32-bit microprocessors are the norm.
The memory bus is the computer bus which connects the main memory to the memory controller in computer systems. Originally, general-purpose buses like VMEbus and the S-100 bus were used, but to reduce latency, modern memory buses are designed to connect directly to DRAM chips, and thus are designed by chip standards bodies such as JEDEC. Examples are the various generations of SDRAM, and serial point-to-point buses like SLDRAM and RDRAM. An exception is the Fully Buffered DIMM which, despite being carefully designed to minimize the effect, has been criticized for its higher latency.
Memory segmentation is a computer (primary) memory management technique of division of a computer's primary memory into segments or sections. In a computer system using segmentation, a reference to a memory location includes a value that identifies a segment and an offset within that segment. Segments or sections are also used in object files of compiled programs when they are linked together into a program image and when the image is loaded into memory.
As one of the first widely available processors with a 32-bit instruction set, and running at relatively high speeds for the era, the 68k was a popular design through the 1980s. It was widely used in a new generation of personal computers with graphical user interfaces, including the Apple Macintosh, Commodore Amiga, Atari ST and many others. It competed primarily against the Intel 8088, found in the IBM PC, which it easily outperformed. The 68k and 8088 pushed other designs, like the Zilog Z8000 and National Semiconductor 32016, into niche markets, and made Motorola a major player in the CPU space.
A personal computer (PC) is a multi-purpose computer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or technician. Unlike large costly minicomputer and mainframes, time-sharing by many people at the same time is not used with personal computers.
The graphical user interface is a form of user interface that allows users to interact with electronic devices through graphical icons and visual indicators such as secondary notation, instead of text-based user interfaces, typed command labels or text navigation. GUIs were introduced in reaction to the perceived steep learning curve of command-line interfaces (CLIs), which require commands to be typed on a computer keyboard.
The Macintosh is a family of personal computers designed, manufactured and sold by Apple Inc. since January 1984.
The 68k was soon expanded with additional family members, implementing full 32-bit ALUs as part of the growing Motorola 68000 series. The original 68k is generally software forward-compatible with the rest of the line despite being limited to a 16-bit wide external bus. years in production, the 68000 architecture is still in use.After 40
The Motorola 68000 series is a family of 32-bit CISC microprocessors. During the 1980s and early 1990s, they were popular in personal computers and workstations and were the primary competitors of Intel's x86 microprocessors. They were most well known as the processors powering the early Apple Macintosh, the Commodore Amiga, the Sinclair QL, the Atari ST, the Sega Genesis, and several others. Although no modern desktop computers are based on processors in the 68000 series, derivative processors are still widely used in embedded systems.
Forward compatibility or upward compatibility is a design characteristic that allows a system to accept input intended for a later version of itself. The concept can be applied to entire systems, electrical interfaces, telecommunication signals, data communication protocols, file formats, and computer programming languages. A standard supports forward compatibility if a product that complies with earlier versions can "gracefully" process input designed for later versions of the standard, ignoring new parts which it does not understand.
Semiconductor device fabrication is the process used to create the MOSFET semiconductor devices used in the integrated circuits (ICs) that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is almost always used, but various compound semiconductors are used for specialized applications.
Motorola's first widely-produced CPU was the Motorola 6800. Although a capable design, it was eclipsed by more powerful designs like the Zilog Z80 and less powerful but faster designs like the MOS 6502. As the sales prospects of the 6800 dimmed, Motorola began a totally new design to replace it. This became the Motorola Advanced Computer System on Silicon project, or MACSS, begun in 1976.
The Z80 is an 8-bit microprocessor introduced by Zilog as the startup company's first product. The Z80 was conceived by Federico Faggin in late 1974 and developed by him and his 11 employees starting in early 1975. The first working samples were delivered in March 1976, and it was officially introduced on the market in July 1976. With the revenue from the Z80, the company built its own chip factories and grew to over a thousand employees over the following two years.
The MOS Technology 6502 is an 8-bit microprocessor that was designed by a small team led by Chuck Peddle for MOS Technology. When it was introduced in 1975, the 6502 was, by a considerable margin, the least expensive microprocessor on the market. It initially sold for less than one-sixth the cost of competing designs from larger companies, such as Motorola and Intel, and caused rapid decreases in pricing across the entire processor market. Along with the Zilog Z80, it sparked a series of projects that resulted in the home computer revolution of the early 1980s.
The MACSS aimed to develop an entirely new architecture without backward compatibility with the 6800. It ultimately 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 68000 design 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 MACSS team drew heavily on the influence of minicomputer processor design, such as the PDP-11 and VAX systems, which were similarly microcode-based.
Backward compatibility is a property of a system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especially in telecommunications and computing. Backward compatibility is sometimes also called downward compatibility.
An instruction set architecture (ISA) is an abstract model of a computer. It is also referred to as architecture or computer architecture. A realization of an ISA is called an implementation. An ISA permits multiple implementations that may vary in performance, physical size, and monetary cost ; because the ISA serves as the interface between software and hardware. Software that has been written for an ISA can run on different implementations of the same ISA. This has enabled binary compatibility between different generations of computers to be easily achieved, and the development of computer families. Both of these developments have helped to lower the cost of computers and to increase their applicability. For these reasons, the ISA is one of the most important abstractions in computing today.
A minicomputer, or colloquially mini, is a class of smaller computers that was developed in the mid-1960s and sold for much less than mainframe and mid-size computers from IBM and its direct competitors. In a 1970 survey, The New York Times suggested a consensus definition of a minicomputer as a machine costing less than US$25,000, with an input-output device such as a teleprinter and at least four thousand words of memory, that is capable of running programs in a higher level language, such as Fortran or BASIC. The class formed a distinct group with its own software architectures and operating systems. Minis were designed for control, instrumentation, human interaction, and communication switching as distinct from calculation and record keeping. Many were sold indirectly to original equipment manufacturers (OEMs) for final end use application. During the two decade lifetime of the minicomputer class (1965–1985), almost 100 companies formed and only a half dozen remained.
In the mid 1970s, the 8-bit microprocessor 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. Intel had worked on their advanced 16/32-bit Intel iAPX 432 (alias 8800) since 1975 and their Intel 8086 since 1976 (it was introduced in 1978 but became really widespread in the form of the almost identical 8088 in the IBM PC a few years later). Arriving late to the 16-bit arena afforded the new processor more transistors (roughly 40,000[ citation needed ] active versus 20,000 active in the 8086), 32-bit macroinstructions, and acclaimed general ease of use.
The original MC68000 was fabricated using an HMOS process with a 3.5 µm feature size. Formally introduced in September 1979, initial samples were released in February 1980, with production chips available over the counter in November. Initial speed grades were 4, 6, and 8 MHz. 10 MHz chips became available during 1981[ citation needed ], and 12.5 MHz chips by June 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.
The 68k instruction set was particularly well suited to implement Unix,and the 68000 and its successors became the dominant CPUs for Unix-based workstations including Sun workstations and Apollo/Domain workstations. The 68000 also was used for mass-market computers such as the Apple Lisa, Macintosh, Amiga, and Atari ST. The 68000 was used in Microsoft Xenix systems, as well as an early NetWare Unix-based Server. The 68000 was used in the first generation of desktop laser printers, including the original Apple Inc. LaserWriter and the HP LaserJet.
In 1982, the 68000 received a minor update to its ISA to support virtual memory and to conform to the Popek and Goldberg virtualization requirements. The updated chip was called the 68010. It also added a new "loop mode" which sped up small loops, and increased overall performance by about 10% at the same clock speeds. A further extended version, which exposed 31 bits of the address bus, was also produced in small quantities as the 68012.
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.
Several other companies were second-source manufacturers of the HMOS 68000. These included Hitachi (HD68000), who shrank the feature size to 2.7 µm for their 12.5 MHz version, 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).
Encrypted variants of the 68000, being the Hitachi FD1089 and FD1094, store decryption keys for opcodes and opcode data in battery-backed memory and were used in certain Sega arcade systems including System 16 to prevent piracy and illegal bootleg games.
The 68HC000, the first CMOS version of the 68000, was designed by Hitachi and jointly introduced in 1985. 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.) Apple selected the 68HC000 for use in the Macintosh Portable.Motorola's version was called the MC68HC000, while Hitachi's was the HD68HC000. The 68HC000 was eventually offered at speeds of 8–20
Motorola replaced the MC68008 with the MC68HC001 in 1990.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.
The later evolution of the 68000 focused on more modern embedded control applications and on-chip peripherals. The 68EC000 chip and SCM68000 core expanded the address bus to 32 bits, removed the M6800 peripheral bus, and excluded the MOVE from SR instruction from user mode programs. In 1996, Motorola updated the standalone core with fully static circuitry, drawing only 2 µW in low-power mode, calling it the MC68SEC000.
Motorola ceased production of the HMOS MC68000 and MC68008 in 1996,but its spin-off company Freescale Semiconductor was 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, were also still in production. More recently, with the Sendai fab closure, all 68HC000, 68020, 68030, and 68882 parts have been discontinued, leaving only the 68SEC000 in production.
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.
At its introduction, the 68000 was first used in high-priced systems, including multiuser microcomputers like the WICAT 150,early Alpha Microsystems computers, Sage II / IV, 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. Unix systems rapidly moved to the more capable later generations of the 68k line, which remained popular in that market throughout the 1980s.
By the mid-1980s, falling production cost made the 68000 viable for use in personal and home computers, starting with the Apple Lisa and Macintosh, and followed by the Commodore Amiga, Atari ST, and Sharp X68000. On the other hand, the Sinclair QL microcomputer was the most commercially important utilisation of the 68008, along with its derivatives, such as the ICL One Per Desk business terminal. Helix Systems (in Missouri, United States) designed an extension to the SWTPC SS-50 bus, the SS-64, and produced systems built around the 68008 processor.
While the adoption of RISC and x86 displaced the 68000 series as desktop/workstation CPU, the processor found substantial use in embedded applications. By the early 1980s, quantities of 68000 CPUs could be purchased for less than 30 USD per part.
Video game manufacturers used the 68000 as the backbone of many arcade games and home game consoles: Atari's Food Fight , from 1982, was one of the first 68000-based arcade games. Others included Sega's System 16, Capcom's CP System and CPS-2, and SNK's Neo Geo. By the late 1980s, the 68000 was inexpensive enough to power home game consoles, such as Sega's Mega Drive/Genesis console and also the Sega CD attachment for it (A Sega CD system has three CPUs, two of them 68000s). The 1993 multi-processor Atari Jaguar console used a 68000 as a support chip, although some developers used it as the primary processor due to familiarity. The 1994 multi-processor Sega Saturn console used the 68000 as a sound co-processor (much as the Mega Drive/Genesis uses the Z80 as a co-processor for sound and/or other purposes).
Certain arcade games (such as Steel Gunner and others based on Namco System 2) use a dual 68000 CPU configuration,and systems with a triple 68000 CPU configuration also exist (such as Galaxy Force and others based on the Sega Y Board), along with a quad 68000 CPU configuration, which has been used by Jaleco (one 68000 for sound has a lower clock rate compared to the other 68000 CPUs) for games such as Big Run and Cisco Heat ; a fifth 68000 (at a different clock rate compared to the other 68000 CPUs) was additionally used in the Jaleco arcade game Wild Pilot for I/O processing.
The 68000 also saw great success as an embedded controller. As early as 1981, laser printers such as the Imagen Imprint-10 were controlled by external boards equipped with the 68000. The first HP LaserJet—introduced in 1984—came with a built-in 8 MHz 68000. Other printer manufacturers adopted the 68000, including Apple with its introduction of the LaserWriter in 1985, the first PostScript laser printer. The 68000 continued to be widely used in printers throughout the rest of the 1980s, persisting well into the 1990s in low-end printers.
The 68000 also saw success in the field of industrial control systems. Among the systems 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.
In a number of digital oscilloscopes from the 80s,the 68000 has been used as a waveform display processor; some models including the LeCroy 9400/9400A also use the 68000 as a waveform math processor (including addition, subtraction, multiplication, and division of two waveforms/references/waveform memories), and some digital oscilloscopes using the 68000 (including the 9400/9400A) can also perform FFT functions on a waveform.
The 683XX microcontrollers, based on the 68000 architecture, are used in networking and telecom equipment, television set-top boxes, laboratory and medical instruments, and even handheld calculators. The MC68302 and its derivatives have been used in many telecom products from Cisco, 3com, Ascend, Marconi, Cyclades and others. Past models of the Palm PDAs and the Handspring Visor used the DragonBall, a derivative of the 68000. AlphaSmart uses the DragonBall family in later versions of its portable word processors. 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.
A modified version of the 68000 formed the basis of the IBM XT/370 hardware emulator of the System 370 processor.
|Motorola 68000 registers|
The 68000 has a 24-bit external address bus and two byte-select signals "replaced" A0. These 24 lines can therefore address 16 MB of physical memory with byte resolution. Address storage and computation uses 32 bits internally; however, the 8 high-order address bits are ignored due to the physical lack of device pins. This allows it to run software written for a logically flat 32-bit address space, while accessing only a 24-bit physical address space. Motorola's intent with the internal 32-bit address space was forward compatibility, making it feasible to write 68000 software that would take full advantage of later 32-bit implementations of the 68000 instruction set.
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 68000 implementations. For example, early (pre-7.0) versions of Apple's Mac OS used the high byte of memory-block master pointers to hold flags such as locked and purgeable. Later versions of the OS moved the flags to a nearby location, and Apple began shipping computers which had "32-bit clean" ROMs beginning with the release of the 1989 Mac IIci.
The 68000 family stores multi-byte integers in memory in big-endian order.
The CPU has eight 32-bit general-purpose data registers (D0-D7), and eight address registers (A0-A7). The last address register is the stack pointer, and assemblers accept the label SP as equivalent to A7. This was a good number of registers at the time in many ways. It was small enough to allow the 68000 to respond quickly to interrupts (even in the worst case where all 8 data registers D0–D7 and 7 address registers A0–A6 needed to be saved, 15 registers in total), and yet large enough to make most calculations fast, because they could be done entirely within the processor without keeping any partial results in memory. (Note that an exception routine in supervisor mode can also save the user stack pointer A7, which would total 8 address registers. However, the dual stack pointer (A7 and supervisor-mode A7') design of the 68000 makes this normally unnecessary, except when a task switch is performed in a multitasking system.)
Having two types of registers was mildly annoying at times, but not hard to use in practice. Reportedly[ citation needed ], it allowed the CPU designers to achieve a higher degree of parallelism, by using an auxiliary execution unit for the address registers.
The 68000 comparison, arithmetic, and logic operations set bit flags in a status register to record their results for use by later conditional jumps. The bit flags are "zero" (Z), "carry" (C), "overflow" (V), "extend" (X), and "negative" (N). The "extend" (X) flag deserves special mention, because it is separate from the carry flag. This permits the extra bit from arithmetic, logic, and shift operations to be separated from the carry for flow-of-control and linkage.
The designers attempted to make the assembly language orthogonal. That is, instructions are divided into operations and address modes, and almost all address modes are available for almost all instructions. There are 56 instructions and a minimum instruction size of 16 bits. Many instructions and addressing modes are longer to include additional address or mode bits.
The CPU, and later the whole family, implements two levels of privilege. User mode gives access to everything except privileged instructions such as interrupt level controls.Supervisor privilege gives access to everything. An interrupt always becomes supervisory. The supervisor bit is stored in the status register, and is visible to user programs.
An advantage of this system is that the supervisor level has a separate stack pointer. This permits a multitasking system to use very small stacks for tasks, because the designers do not have to allocate the memory required to hold the stack frames of a maximum stack-up of interrupts.
The CPU recognizes seven interrupt levels. Levels 1 through 5 are strictly prioritized. That is, a higher-numbered interrupt can always interrupt a lower-numbered interrupt. In the status register, a privileged instruction allows one to set the current minimum interrupt level, blocking lower or equal priority interrupts. For example, if the interrupt level in the status register is set to 3, higher levels from 4 to 7 can cause an exception. Level 7 is a level triggered non-maskable interrupt (NMI). Level 1 can be interrupted by any higher level. Level 0 means no interrupt. The level is stored in the status register, and is visible to user-level programs.
Hardware interrupts are signalled to the CPU using three inputs that encode the highest pending interrupt priority. A separate Encoder 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 (used in the Atari ST range of computers and Sharp X68000), which also provided a UART, timer, and parallel I/O.
The "exception table" (interrupt vector table interrupt vector addresses) is fixed at addresses 0 through 1023, permitting 256 32-bit vectors. The first vector (RESET) consists of two vectors, namely the starting stack address, and the starting code address. Vectors 3 through 15 are used to report various errors: bus error, address error, illegal instruction, zero division, CHK and CHK2 vector, privilege violation (to block privilege escalation), and some reserved vectors that became line 1010 emulator, line 1111 emulator, and hardware breakpoint. Vector 24 starts the real interrupts: spurious interrupt (no hardware acknowledgement), and level 1 through level 7 autovectors, then the 16 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.
The 68000 does not meet the Popek and Goldberg virtualization requirements for full processor virtualization because it has a single unprivileged instruction "MOVE from SR", which allows user-mode software read-only access to a small amount of privileged state.
The 68000 is 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.
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 push 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 is provided for use in its place by user mode software; an operating system can trap and emulate user-mode MOVE from SR instructions if desired.
The standard addressing modes are:
Plus: access to the status register, and, in later models, other special registers.
Most instructions have dot-letter suffixes, permitting operations to occur on 8-bit bytes (".b"), 16-bit words (".w"), and 32-bit longs (".l").
Like many CPUs of its era the cycle timing of some instructions varied depending on the source operand(s). For example, the unsigned multiply instruction takes (38+2n) clock cycles to complete where 'n' is equal to the number of bits set in the operand.To create a function that took a fixed cycle count required the addition of extra code after the multiply instruction. This would typically consume extra cycles for each bit that wasn't set in the original multiplication operand.
Most instructions are dyadic , that is, the operation has a source, and a destination, and the destination is changed. Notable instructions were:
The 68EC000 is a low-cost version of the 68000 with a slightly different pinout, designed for embedded controller applications. The 68EC000 can have either a 8-bit or 16-bit data bus, switchable at reset.
The processors are available in a variety of speeds including 8 and 16 MHz configurations, producing 2,100 and 4,376 Dhrystones each. These processors have no floating-point unit, and it is difficult to implement an FPU coprocessor (MC68881/2) with one because the EC series lacks necessary coprocessor instructions.
The 68EC000 was used as a controller in many audio applications, including Ensoniq musical instruments and sound cards, where it was part of the MIDI synthesizer.On Ensoniq sound boards, the controller provided several advantages compared to competitors without a CPU on board. The processor allowed the board to be configured to perform various audio tasks, such as MPU-401 MIDI synthesis or MT-32 emulation, without the use of a TSR program. This improved software compatibility, lowered CPU usage, and eliminated host system memory usage.
The Motorola 68EC000 core was later used in the m68k-based DragonBall processors from Motorola/Freescale.
It also was used as a sound controller in the Sega Saturn game console and as a controller for the HP JetDirect Ethernet controller boards for the mid-1990s LaserJet printers.
The 68000 assembly code below is for a subroutine named
strtolower, which copies a null-terminated string of 8-bit characters to a destination string, converting all alphabetic characters to lower case.
00100000 00100000 4E56 0000 00100004 306E 0008 00100008 326E 000C 0010000C 1018 0010000E 0C40 0041 00100012 6500 000E 00100016 0C40 005A 0010001A 6200 0006 0010001E 0640 0020 00100022 12C0 00100024 66E6 00100026 4E5E 00100028 4E75 0010002A
; strtolower:; Copy a null-terminated ASCII string, converting; all alphabetic characters to lower case.;; Entry parameters:; (SP+0): Source string address; (SP+4): Target string addressorg$00100000;Start at 00100000strtolowerpubliclinka6,#0;Set up stack framemovea8(a6),a0;A0 = src, from stackmovea12(a6),a1;A1 = dst, from stackloopmove.b(a0)+,d0;Load D0 from (src), incr srccmpi#'A',d0;If D0 < 'A',blocopy;skipcmpi#'Z',d0;If D0 > 'Z',bhicopy;skipaddi#'a'-'A',d0;D0 = lowercase(D0)copymove.bd0,(a1)+;Store D0 to (dst), incr dstbneloop;Repeat while D0 <> NULunlka6;Restore stack framerts;Returnend
The subroutine establishes a call frame using register A6 as the frame pointer. This kind of calling convention supports reentrant and recursive code and is typically used by languages like C and C++. The subroutine then retrieves the parameters passed to it (
dst) from the stack. It then loops, reading an ASCII character (a single byte) from the
src string, checking whether it is a capital alphabetic character, and if so, converting it into a lower-case character, otherwise leaving it as it is, then writing the character into the
dst string. Finally, it checks whether the character was a null character; if not, it repeats the loop, otherwise it restores the previous stack frame (and A6 register) and returns. Note that the string pointers (registers A0 and A1) are auto-incremented in each iteration of the loop.
In contrast, the code below is for a stand-alone function, even on the most restrictive version of AMS for the TI-89 series of calculators, being kernel-independent, with no values looked up in tables, files or libraries when executing, no system calls, no exception processing, minimal registers to be used, nor the need to save any. It is valid for historical Julian dates from 1 March 1 AD, or for Gregorian ones. In less than two dozen operations it calculates a day number compatible with ISO 8601 when called with three inputs stored at their corresponding LOCATIONS:
; ; WDN, an address - for storing result d0 ; FLAG, 0 or 2 - to choose between Julian or Gregorian, respectively ; DATE, year0mda - date stamp as binary word&byte&byte in basic ISO-format ;(YEAR, year ~ YEAR=DATE due to big-endianness) ; move.l DATE,d0 move.l d0,d1 ; ; Apply step 1 - Lachman's method of congruence andi.l #$f00,d0 divu #100,d0 addi.w #193,d0 andi.l #$ff,d0 divu #100,d0 ; d0 contains the month index in the upper word ; ; Apply step 2 - Using spqr as the Julian year of the last leap day swap d0 andi.l #$ffff,d0 add.b d1,d0 add.w YEAR,d0 subi.l #$300,d1 lsr #2,d1 swap d1 add.w d1,d0 ; spqr/4 + year + mi + da ; ; (Apply step 0 - Gregorian adjustment) mulu FLAG,d1 divu #50,d1 mulu #25,d1 lsr #2,d1 add.w d1,d0 add.w FLAG,d0 ; (sp32div16) + spqr/4 + year + mi + da ; divu #7,d0 swap d0 ; d0.w becomes the day number ; move.w d0,WDN ; returns the day number to address WDN rts ; ; Days of the week correspond to day numbers of the week as: ; Sun=0 Mon=1 Tue=2 Wed=3 Thu=4 Fri=5 Sat=6 ;
The Intel 8080 ("eighty-eighty") was the second 8-bit microprocessor designed and manufactured by Intel and was released in April 1974. It is an extended and enhanced variant of the earlier 8008 design, although without binary compatibility. The initial specified clock rate or frequency limit was 2 MHz, and with common instructions using 4, 5, 7, 10, or 11 cycles this meant that it operated at a typical speed of a few hundred thousand instructions per second. A faster variant 8080A-1 became available later with clock frequency limit up to 3.125 MHz.
The 8086 is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-bit data bus, and is notable as the processor used in the original IBM PC design, including the widespread version called IBM PC XT.
The Intel 8088 microprocessor is a variant of the Intel 8086. Introduced on June 1, 1979, the 8088 had an eight-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers and the one megabyte address range were unchanged, however. In fact, according to the Intel documentation, the 8086 and 8088 have the same execution unit (EU)—only the bus interface unit (BIU) is different. The original IBM PC was based on the 8088, as were its clones.
The Motorola 68020 is a 32-bit microprocessor from Motorola, released in 1984. It is the successor to the Motorola 68010 and is succeeded by the Motorola 68030. A lower cost version was also made available, known as the 68EC020. In keeping with naming practices common to Motorola designs, the 68020 is usually referred to as the "020", pronounced "oh-two-oh" or "oh-twenty".
The Motorola 6809 ("sixty-eight-oh-nine") is an 8-bit microprocessor CPU with some 16-bit features from Motorola. It was designed by Terry Ritter and Joel Boney and introduced in 1978. It was a major advance over both its predecessor, the Motorola 6800, and the related MOS Technology 6502. Among the systems to use the 6809 are the Dragon home computers, TRS-80 Color Computer, the Vectrex home console, and early 1980s arcade machines including Defender, Robotron: 2084, Joust, and Gyruss. More modern systems that utilize a synthesized 6809 core (HDL) are the CoCo3FPGA, Matchbox CoCo, CoCoDEV and Multicomp.
The 68HC11 is an 8-bit microcontroller (µC) family introduced by Motorola in 1984. Now produced by NXP Semiconductors, it descended from the Motorola 6800 microprocessor by way of the 6809. It is a CISC microcontroller. The 68HC11 devices are more powerful and more expensive than the 68HC08 microcontrollers, and are used in automotive applications, barcode readers, hotel card key writers, amateur robotics, and various other embedded systems. The MC68HC11A8 was the first microcontroller to include CMOS EEPROM.
The NS32000, sometimes known as the 32k, is a series of microprocessors produced by National Semiconductor. The first member of the family, the 32016, came to market in 1982, making it the first 32-bit general-purpose microprocessor on the market. However, the 32016 contained a large number of bugs and often could not be run at its rated speed. These problems, and the presence of the similar Motorola 68000, led to almost no use in the market.
The Motorola MC68010 processor is a 16/32-bit microprocessor from Motorola, released in 1982 as the successor to the Motorola 68000. It fixes several small flaws in the 68000, and adds a few features.
In computer architecture, 64-bit computing is the use of processors that have datapath widths, integer size, and memory address widths of 64 bits. Also, 64-bit computer architectures for central processing units (CPUs) and arithmetic logic units (ALUs) are those that are based on processor registers, address buses, or data buses of that size. From the software perspective, 64-bit computing means the use of code with 64-bit virtual memory addresses. However, not all 64-bit instruction sets support full 64-bit virtual memory addresses; x86-64 and ARMv8, for example, support only 48 bits of virtual address, with the remaining 16 bits of the virtual address required to be all 0's or all 1's, and several 64-bit instruction sets support fewer than 64 bits of physical memory address.
The Motorola 68008 is an 8/16/32-bit microprocessor made by Motorola. It is a version of the Motorola 68000 with an 8-bit external data bus, as well as a smaller address bus.
The Z8000 is a 16-bit microprocessor introduced by Zilog in early 1979. The architecture was designed by Bernard Peuto while the logic and physical implementation was done by Masatoshi Shima, assisted by a small group of people.
Addressing modes are an aspect of the instruction set architecture in most central processing unit (CPU) designs. The various addressing modes that are defined in a given instruction set architecture define how machine language instructions in that architecture identify the operand(s) of each instruction. An addressing mode specifies how to calculate the effective memory address of an operand by using information held in registers and/or constants contained within a machine instruction or elsewhere.
The Signetics 2650 was an 8-bit microprocessor introduced in mid-1975. According to Adam Osborne's book An Introduction to Microprocessors Vol 2: Some Real Products, it was "the most minicomputer-like" of the microprocessors available at the time.
The 9S08 is a 8-bit microcontroller (µC) family originally produced by Motorola, later by Freescale Semiconductor, and currently by NXP, descended from the Motorola 6800 microprocessor. It is a CISC microcontroller. A slightly extended variant of the 68HC08, it shares upward compatibility with the aging 68HC05 microcontrollers, and is found in almost any type of embedded systems. The larger members offer up to 128 KiB of flash, and 8 KiB of RAM via a simple MMU which allows bank-switching 16 KiB of the address space and an address/data register pair which allows data fetches from any address. The paging scheme used allows for a theoretical maximum of 4MB of flash.
In computer architecture, 16-bit integers, memory addresses, or other data units are those that are 16 bits wide. Also, 16-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. 16-bit microcomputers are computers in which 16-bit microprocessors were the norm.
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