The Motorola 6809 is an 8-bit (arguably, an 8/16-bit) microprocessor CPU from Motorola, introduced circa 1979. Eight-bit CPUs normally use an 8-bit data bus and a 16-bit address bus which means that their Address space is limited to 64 KBs This is not a "natural 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. It was a major advance over both its predecessor, the Motorola 6800, and the related, MOS Technology 6502. The 6800 is an 8-bit Microprocessor produced by Motorola and released shortly after the Intel 8080 in late 1974 The MOS Technology 6502 is an 8-bit Microprocessor that was designed by Chuck Peddle for MOS Technology in 1975
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Description
Among the significant enhancements introduced in the 6809 were the use of two 8-bit accumulators (A and B, which could be combined into a single 16-bit register, D), two 16-bit index registers (X, Y) and two 16-bit stack pointers (U, S). In a Computer 's central processing unit ( CPU) an accumulator is a register in which intermediate arithmetic and logic results are stored In Computer architecture, a processor register is a small amount of storage available on the CPU whose contents can be accessed more quickly than storage An index register in a computer's CPU is a Processor register used for modifying Operand addresses during the run of a program typically for doing vector/ In Computer science, a stack is an Abstract data type and Data structure based on the principle of Last In First Out (LIFO The index and stack registers allowed very advanced addressing modes. Addressing modes are an aspect of the Instruction set architecture in most Central processing unit (CPU designs
The 6809 was source-compatible with the 6800, though the 6800 had seventy-eight instructions to the 6809's fifty-nine. Some instructions were replaced by more general ones which the assembler translated into equivalent operations and some were even replaced by addressing modes. See the terminology section below for information regarding inconsistent use of the terms assembly and assembler Addressing modes are an aspect of the Instruction set architecture in most Central processing unit (CPU designs The instruction set and register complement were highly orthogonal, making the 6809 easier to program than the 6800 or 6502. An instruction set is a list of all the instructions and all their variations that a processor can execute In Mathematics, two Vectors are orthogonal if they are Perpendicular, i
Other features were one of the first hardware-implementations of a multiplication instruction in an MPU, full 16-bit arithmetic and an especially fast interrupt system. In Computing, an interrupt is an asynchronous signal from hardware indicating the need for attention or a synchronous event in software indicating the need for a change The 6809 was also highly optimized, up to five times faster than the 6800 series CPUs. Like the 6800, it included an undocumented address bus test instruction that would exceed the limits of some memory controllers, evoking the nickname Halt and Catch Fire (HCF). Halt and Catch Fire, known by the Mnemonic HCF, was originally a fictitious computer Machine code instruction claimed to be under development at IBM
The 6809's state machine and control logic, unlike many processors of the day, was mostly implemented using a large PLA and asynchronous random logic (a common trait of early designs as well as RISC CPUs) rather than microcoded. A programmable logic array (PLA is a programmable device used to implement combinational Logic circuits. To execute instructions a Computer 's Processor must generate the control signals used to perform the processor's actions in the proper sequence Microprogramming (ie writing microcode) is a method that can be employed to implement Machine instructions in a CPU relatively easily often using less This means it used only one clock cycle per machine cycle and therefore fewer clock cycles per instruction compared to the Z80 for instance, one of the 6809's main competitors. In Electronics and especially synchronous Digital circuits a clock signal is a signal used to coordinate the actions of two or more circuits The Zilog Z80 is an 8-bit Microprocessor designed and sold by Zilog from July 1976 onwards For example, the instruction ADDA 63 took three clock cycles, compared to the seven clock cycles of ADD A,63 on a Z80, which therefore needs at least twice the clock speed to match the 6809 on this particular operation. However, the more synchronous Z80 design could typically employ 3-5 times the clock frequency of the 6809, 6800, or 6502 without demanding faster memory chips (often the limiting factor). This is because these largely asynchronous designs allows only approximately half a clock cycle for actual memory access (see data sheets), while the high resolution state machine in the Z80 can combine 2-3 (short) clock cycles into a relatively long memory access period.
The 6809 had an internal clock generator (needing only an external crystal) whereas the 6809E needed an external clock generator. There were also variants such as the 68A09(E) and 68B09(E); the internal letter indicates the processor's rated clock speed.
History
The Motorola 6809 was originally produced in 1 MHz, 1. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. 5 MHz (68A09) and 2 MHz (68B09) speed ratings. Faster versions were produced later by Hitachi and perhaps others. It is sometimes considered to be the conceptual precursor of the Motorola 68000 family of processors, though this is mostly a misunderstanding. The Motorola 68000 is a 16/32-bit CISC Microprocessor core designed and marketed by Freescale Semiconductor (formerly Motorola Semiconductor The 6809 and 68000 design projects ran largely in parallel and both processors were released in 1979. There is a certain amount of design philosophy similarity (eg, considerable orthogonality and flexible addressing modes), some assembly language syntax resemblance, as well as opcode mnemonic similarity, but the 6809 is a derivative of the 6800 whereas the 68000 was a totally new design. See the terminology section below for information regarding inconsistent use of the terms assembly and assembler An 8-bit data bus version of the 68000 (ie, the 68008) was intended for use in future 8-bit designs. The Motorola 68008 is an 8/16/32-bit Microprocessor made by Motorola. In that respect, the 6809 was rather quickly an evolutionary dead-end.
The 6809 design team believed that future system integrators would look to off-the-shelf code in ROMs to handle common tasks. An example of this might be binary floating point arithmetic, which is a common requirement in many systems. In Computing, floating point describes a system for numerical representation in which a string of digits (or Bits represents a Real number. In order to speed time to market, common code modules would be purchased, rather than developed in-house, and integrated into systems with code from other manufacturers. Since a CPU designer could hardly guarantee where this code would be located in a future system, the 6809 design focused heavily on support of position-independent, reentrant code that could be freely located anywhere in the memory map. In Computing, position-independent code ( PIC) or position-independent executable ( PIE) is machine instruction code that executes properly This expectation was, in reality, never quite met: Motorola's only released example of a ROM'd software module was the MC6839 floating-point ROM. However, the decisions made by the design team made for a very powerful processor and made possible advanced operating systems like OS-9 and UniFlex, which took advantage of the position-independent, re-entrant nature of the 6809. OS-9 is a family of real-time, process-based, multitasking, Multi-user, Unix-like Operating systems developed in the 1980s UniFlex is Unix-like Operating system developed by Technical Systems Consultants (TSC for Multitasking, Multiprocessing for the
The 6809 was used in Commodore's dual-CPU SuperPET computer, and, in its 68A09 incarnation, in the unique vector graphics based Vectrex home video game console with built-in screen display. The PET ( P ersonal E lectronic T ransactor) was a home -/ Personal computer produced by Commodore starting in 1977 The Vectrex is an 8-bit Video game console that was developed by Western Technologies/Smith Engineering. The 6809E was used in the TRS-80 Color Computer (CoCo), the Acorn System 2, 3 and 4 computers (as an optional alternative to their standard 6502) and in the CoCo's UK clone, the Welsh-made Dragon 32/64 home computers, and the SWTPC, Gimix, Smoke Signal Broadcasting, etc SS-50 bus systems, in addition to several of Motorola's own EXORmacs development systems. The Radio Shack TRS-80 Color Computer (also called Tandy Color Computer, or CoCo) was a Home computer launched in 1980 The System 2 was a home computer produced by Acorn Computers from 1980. The MOS Technology 6502 is an 8-bit Microprocessor that was designed by Chuck Peddle for MOS Technology in 1975 This article is about the Dragon home computers. For other uses see Dragon (disambiguation. The US company SWTPC started in 1964 as DEMCO (Daniel E Meyer Company In France, Thomson micro-informatique produced a series of micro-computers based on the 6809E (TO7, TO7/70, TO8, TO8D, TO9, TO9Plus, MO5, MO6, MO5E and MO5NR). Thomson SA (,) formerly known as Thomson Multimedia is an international provider of solutions for the creation management delivery and access of video for the The Thomson MO5 was an 6809 -based Computer designed in 1984 The MO-5 was replaced by the MO-6 in
In addition to home computers and game consoles, the 6809 was also utilized in a number of arcade games released during the early to mid 1980s. Williams Electronics was an especially prolific user of the processor, which was deployed in arcade hits such as Defender, Joust, Sinistar, and Robotron: 2084. WMS Industries Inc ( is a long-standing American electronic gaming and amusement company based in Waukegan Illinois. Joust is an Arcade game produced by Williams Electronics in 1982 Sinistar is an Arcade game released by Williams in 1982 It belongs to a class of Video games from the 1980s called " Twitch games Robotron 2084 (often called simply Robotron) is an Arcade game created in 1982 by the company Vid Kidz ( Eugene Jarvis Williams also utilized the processor in many of its solid-state pinball machines; a specialized version of the 6809 CPU formed the core of the successful Williams Pinball Controller. Pinball is a type of coin-operated Arcade game where a player attempts to score points by manipulating one or more Metal balls on a playfield inside a Glass The Williams Pinball Controller (WPC is an Arcade system board used for several Pinball games designed by Williams and Midway (under the
Software development company Microware developed the original OS-9 operating system (not to be confused with the more recent Mac OS 9) for the 6809, later porting it to the 68000 and i386 series of microprocessors. Microware is a US corporation that produced the OS-9 real-time Operating system. OS-9 is a family of real-time, process-based, multitasking, Multi-user, Unix-like Operating systems developed in the 1980s Mac OS 9 is the final major release of Apple's "Classic" Mac OS.
The Hitachi 6309 was an enhanced version of the 6809 with extra registers and additional instructions, including block move, additional multiply instructions and hardware-implemented division. The 6309 is Hitachi's CMOS version of the Motorola 6809 Microprocessor. It was used in unofficially-upgraded CoCo 3 computers and a version of OS-9 was written to take advantages of the 6309's extra features: NitrOS-9.
Hitachi also produced its own 6809-based machines, the MB6890 and later the S1. () is a Multinational corporation specializing in high-technology and services headquartered in Marunouchi Itchome Chiyoda, Tokyo, Japan. These were primarily for the Japanese market, but some were exported to and sold in Australia. For a topic outline on this subject see List of basic Australia topics. There the MB6890 was dubbed the "Peach", probably in ironic reference to the popularity of the Apple II. The S1 was notable in that it contained paging hardware extending the 6809's native 64 kilobyte (64×210 byte) addressing range to a full 1 megabyte (1×220 byte) in 4 KB pages. In Computer Operating systems that have their Main memory divided into pages, paging (sometimes called swapping) is a transfer A kilobyte (derived from the SI prefix Kilo -, meaning 1000 is a unit of Information or Computer storage equal to either 1024 A byte (pronounced "bite" baɪt is the basic unit of measurement of information storage in Computer science. A megabyte is a unit of Information or Computer storage equal to either 106 (1000000 Bytes or 220 (1048576 bytes depending on It was similar in this to machines produced by SWTPC, Gimix, and several other suppliers. The US company SWTPC started in 1964 as DEMCO (Daniel E Meyer Company TSC produced a Unix-like operating system uniFlex which ran only on such machines. UniFlex is Unix-like Operating system developed by Technical Systems Consultants (TSC for Multitasking, Multiprocessing for the OS-9 Level II, also took advantage of such memory management facilities. OS-9 is a family of real-time, process-based, multitasking, Multi-user, Unix-like Operating systems developed in the 1980s Most other computers of the time with more than 64 KB of memory addressing were limited to bank switching where much if not all the 64 KB was simply swapped for another section of memory. Bank switching (also known as "paging" but only loosely related to the ordinary meaning of " Paging " in computing was a technique common in 8-bit
Neither Motorola nor Hitachi produce 6809 processors or derivatives anymore, despite the 6809 being one of the most powerful general-purpose 8-bit CPUs ever produced. Many of its innovative features have since been copied. 6809 cores are available in VHDL and can be programmed into FPGA and used as an embedded processor with speed ratings up to 40 MHz. Some 6809 opcodes also live on in the Freescale embedded processors. Freescale Semiconductor Inc is an American Semiconductor manufacturer
References
- Leventhal, Lance (1981). 6809 Assembly Language Programming. Osborne/McGraw-Hill. ISBN 0-931988-35-7.
- Warren, Carl D (1980). The MC6809 Cookbook. TAB Books, Inc. ISBN 0-8306-9683-0.
External links
- http://koti.mbnet.fi/~atjs/mc6809/ – Collection of 6809 instructions, emulators, tools, debuggers, disassemblers and assemblers
- The BYTE 6809 Articles (Jan–February 1979) (PDF) – By Terry Ritter and Joel Boney, co-designers of the 6809; BYTE magazine reproductions by tim lindner
- news://comp.sys.m6809 – Usenet newsgroup for 6809 enthusiasts
- 6809 Emulator based on the SWTPC 6809 system
- Instruction set reference for 6809/6309 (PDF) By Chris Lomont
This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. Byte magazine was an influential Microcomputer magazine in the late 1970s and throughout the 1980s because of its wide-ranging editorial coverage A newsgroup is a Repository usually within the Usenet system for messages posted from many users in different locations 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
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