The Motorola 68020 is a 32-bit microprocessor from Motorola, released in 1984. The range of Integer values that can be stored in 32 bits is 0 through 4294967295 or −2147483648 through 2147483647 using Two's complement encoding A microprocessor incorporates most or all of the functions of a Central processing unit (CPU on a single Integrated Motorola Inc ( is an American, multinational Fortune 100, Telecommunications company based in Schaumburg Illinois. Year 1984 ( MCMLXXXIV) was a Leap year starting on Sunday (link displays the 1984 Gregorian calendar) It is the successor to the Motorola 68010 and is succeeded by the Motorola 68030. The Motorola MC68010 processor is a 16/32-bit Microprocessor from Motorola, released in 1982. The Motorola 68030 is a 32-bit Microprocessor in Motorola 's 68000 family.
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Description
The 68020 (usually just referred to as the '020, pronounced oh-two-oh or oh-twenty) had 32-bit internal and external data and address buses. A lower cost version, the 68EC020, only had a 24-bit address bus. The 68020 was produced at speeds ranging from 12 MHz to 33 MHz.
Improvements over 68010
The 68020 added many improvements to the 68010 including a 32-bit arithmetic logic unit (ALU), external data bus and address bus, and new instructions and addressing modes. In Computing, an arithmetic logic unit ( ALU) is a Digital circuit that performs Arithmetic and Logical operations The 68020 (and 68030) had a proper three-stage pipeline. Though 68010 had a loop mode, it was little used and 68020 replaced this with a proper instruction cache of 256 bytes, the first 68k series processor to feature onboard cache memory.
The alignment restriction on word and longword data access present in its predecessors was removed with the 68020.
Multiprocessing features
The Motorola multiprocessing model was added with the 68020. This allowed up to eight processors per system to co-operate, these eight could be any number of CPUs, FPUs but a single MMU (either a Motorola 68841 or 68851). The 68851 is an external Memory Management Unit (MMU which is designed to provide paged memory support for the 68010 or 68020. This had some limitation, as each CPU used had to be the same model (not necessarily the same clock) and each FPU has to be the same model (again, not necessarily the same clock) so multiprocessing a 68020/25 with a 68030/25 was not allowed (the 020, for example, could not be aware of the 030's internal MMU) but a 68020/25 with a 68882/33 was perfectly acceptable and quite common. It was, however, extremely uncommon to see more than one CPU or FPU in the same system. Most Unix boxes made with 68020s were simply the '020, an FPU (68881 or 68882) and an MMU (68841 or 68851). Unix (officially trademarked as UNIX, sometimes also written as Unix with Small caps) is a computer Motorola 68881 was a Floating-point Coprocessor chip that was utilized in some computer systems that used the 68020 or 68030 Motorola 68881 was a Floating-point Coprocessor chip that was utilized in some computer systems that used the 68020 or 68030
Instruction set
The new instructions included some minor improvements and extensions to the supervisor state, several instructions for software management of a multiprocessing system (which were removed in the 68060), some support for high-level languages which did not get used much (and was removed from future 680x0 processors), bigger multiply (32×32→64 bits) and divide (64÷32→32 bits quotient and 32 bits remainder) instructions, and bit field manipulations.
Addressing modes
The new addressing modes added scaled indexing and another level of indirection to many of the pre-existing modes, and added quite a bit of flexibility to various indexing modes and operations. Addressing modes are an aspect of the Instruction set architecture in most Central processing unit (CPU designs Addressing modes are an aspect of the Instruction set architecture in most Central processing unit (CPU designs Though it was not intended, these new modes made the 68020 very suitable for page printing; most laser printers in the early '90s had a 68EC020 at their core.
The 68020 had a minimal 256 byte direct-mapped instruction cache, arranged as 64 four-byte entries. Although small, it still made a significant difference in the performance of many applications. The resulting decrease in bus traffic was particularly important in systems relying heavily on DMA. Direct memory access ( DMA) is a feature of modern Computers and Microprocessors that allows certain hardware subsystems within the computer to access system
Usage
The 68020 was used in the Apple Macintosh II and Macintosh LC personal computers, as well as Sun 3 workstations and the Hewlett Packard 8711 Series Network Analyzers. Apple Inc, ( formerly Apple Computer Inc, is an American Multinational corporation with a focus on designing and manufacturing Consumer electronics The Apple Macintosh II was the first personal computer model of the Macintosh II series in the Apple Macintosh line The Macintosh LC (meaning low-cost color) was Apple Computer 's product family of low-end consumer Macintosh Personal computers in the early 1990s A personal computer ( PC) is any Computer whose original sales price size and capabilities make it useful for individuals and which is intended to be operated Sun-3 was the name given to a series of UNIX Computer workstations and servers produced by Sun Microsystems, launched on September 9th 1985 The Commodore Amiga 1200 computer and the Amiga CD32 games console used the cost-reduced 68EC020. Commodore, the commonly used name for Commodore International, was a US-American Electronics company based in West Chester Pennsylvania The Amiga 1200, or A1200, was Commodore International 's third-generation Amiga computer aimed at the home market The Amiga CD32 was the first 32-bit CD-ROM based Video game console released in western Europe and Canada
It is also the processor used on board TGV trains to decode signalling information which is sent to the trains through the rails. The TGV ( t rain à g rande v itesse, French for "high-speed train" is France 's High-speed rail service It is further being used in the flight control systems of the Eurofighter Typhoon combat aircraft. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout
For more information on the instructions and architecture see Motorola 68000. The Motorola 68000 is a 16/32-bit CISC Microprocessor core designed and marketed by Freescale Semiconductor (formerly Motorola Semiconductor
Bibliography
This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. The Free On-line Dictionary of Computing ( FOLDOC) is an online searchable encyclopedic Dictionary of Computing subjects The GNU Free Documentation License ( GNU FDL or simply GFDL) is a Copyleft License for free documentation designed by the Free Software
References
External links
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