Motorola 6800

Motorola 6800

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The 6800 was an 8-bit
The first widely adopted 8-bit microprocessor was the Intel 8080, being used in many hobbyist computers of the late 1970s and early 1980s, often running the CP/M operating system. The Zilog Z80 and the Motorola 6800 were also used in similar computers...

A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

 designed and first manufactured by Motorola
Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...

 in 1974. The MC6800 microprocessor was part of the M6800 Microcomputer System that also included serial and parallel interface ICs
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

Random-access memory
Random access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...

Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...

 and other support chips. A significant design feature was that the M6800 family of ICs required only a single five-volt power supply
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...

 at a time when most other microprocessors required three voltages. The M6800 Microcomputer System was announced in March 1974 and was in full production by the end of that year.

The 6800 architecture and instruction set were influenced by the then popular Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...

The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...

 mini computer. The 6800 has a 16-bit address bus that could directly access 64 KB of memory and an 8-bit bi-directional data bus. It has 72 instructions with seven addressing modes for a total of 192 opcode
In computer science engineering, an opcode is the portion of a machine language instruction that specifies the operation to be performed. Their specification and format are laid out in the instruction set architecture of the processor in question...

s. The original MC6800 could have a clock frequency of up to 1 MHz. Later versions had a maximum clock frequency of 2 MHz.

In addition to the ICs, Motorola also provided a complete assembly language
Assembly language
An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...

 development system
Software development
Software development is the development of a software product...

. The customer could use the software on a remote timeshare
Time-sharing is the sharing of a computing resource among many users by means of multiprogramming and multi-tasking. Its introduction in the 1960s, and emergence as the prominent model of computing in the 1970s, represents a major technological shift in the history of computing.By allowing a large...

 computer or on an in-house mini-computer system. The Motorola EXORciser was a desktop computer
Desktop computer
A desktop computer is a personal computer in a form intended for regular use at a single location, as opposed to a mobile laptop or portable computer. Early desktop computers are designed to lay flat on the desk, while modern towers stand upright...

 built with the M6800 ICs that could be used for prototyping
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...

 and debugging
Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge...

 new designs. An expansive documentation package included datasheets on all ICs, two assembly language programming manuals, and a 700-page application manual that showed how to design a point-of-sale computer terminal
Computer terminal
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 6800 was popular in computer peripherals, test equipment
Electronic test equipment
Electronic test equipment is used to create signals and capture responses from electronic Devices Under Test . In this way, the proper operation of the DUT can be proven or faults in the device can be traced and repaired...

 applications and point-of-sale terminals. The MC6802, introduced in 1977, included 128 bytes of RAM and an internal clock oscillator on chip. The MC6801 and MC6805 included with RAM, ROM and I/O on a single chip were popular in automotive applications.

Motorola's history in semiconductors

Galvin Manufacturing Corporation was founded in 1928 in Chicago, Illinois and produced their first Motorola brand car radio in 1930. The company name was changed to Motorola in 1947. A research and development center was opened in Phoenix, Arizona in 1949 and they began commercial production of transistors at a new $1.5 million facility in Phoenix in 1955. In 1966 an integrated circuit facility was built in the Phoenix suburb of Mesa. In 1973, they announced plans to build a new plant in Austin, Texas to manufacture MOS integrated circuits. The microprocessor group moved from Mesa to Austin in 1975.

Motorola's transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

s and integrated circuits were used in-house for their communication, military, automotive and consumer products and they were also sold to other companies. In the 1960s, Motorola sold a full line of digital ICs that were used in computers, test equipment and industrial controls. By 1970 they were producing metal-oxide semiconductors (MOS) LSI chips as standard products and custom circuits. They also produced semiconductor memories that were used in calculators, point-of-sale terminals and computers. Motorola's sales had reached $1.2 billion in 1973 and they had 64,000 employees. The Semiconductor Products Division (SPD) had sales of $419 million and was the second largest semiconductor company after Texas Instruments. Intel was founded in 1968 and had sales of $66 million in 1973.

In the early 1970s Motorola started a project that developed their first microprocessor, the MC6800. This was followed by single chip microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...

s such as the MC6801 and MC6805. In 1979 the 16-bit
-16-bit architecture:The HP BPC, introduced in 1975, was the world's first 16-bit microprocessor. Prominent 16-bit processors include the PDP-11, Intel 8086, Intel 80286 and the WDC 65C816. The Intel 8088 was program-compatible with the Intel 8086, and was 16-bit in that its registers were 16...

 version of the MC 68000
Motorola 68000
The Motorola 68000 is a 16/32-bit CISC microprocessor core designed and marketed by Freescale Semiconductor...

 microprocessor was introduced, this processor was later extended to 32 bits.

In 1999 Motorola spun off their analog IC, digital IC and transistor business to ON Semiconductor
ON Semiconductor
ON Semiconductor , is a semiconductors supplier company. Products include power and signal management, logic, discrete and custom devices for automotive, communications, computing, consumer, industrial, LED lighting, medical, military/aerospace and power applications...

 of Phoenix Arizona. In 2004 they spun off their microprocessor business to Freescale Semiconductor
Freescale Semiconductor
Freescale Semiconductor, Inc. is a producer and designer of embedded hardware, with 17 billion semiconductor chips in use around the world. The company focuses on the automotive, consumer, industrial and networking markets with its product portfolio including microprocessors, microcontrollers,...

 of Austin, Texas.

Development team

Motorola did not chronicle the development of the 6800 microprocessor the way that Intel did for their microprocessors. In 2008 the Computer History Museum
Computer History Museum
The Computer History Museum is a museum established in 1996 in Mountain View, California, USA. The Museum is dedicated to preserving and presenting the stories and artifacts of the information age, and exploring the computing revolution and its impact on our lives.-History:The museum's origins...

 interviewed four members of the 6800 microprocessor design team. Their recollections can be confirmed and expanded by magazine and journal articles written at the time.

The Motorola microprocessor project began in 1971 with a team composed of designer Tom Bennett, engineering director Jeff LaVell, product marketer Link Young and systems designers Mike Wiles, Gene Schriber and Doug Powell. They were all located in Mesa, Arizona. By the time the project was finished, Bennett had 17 chip designers and layout people working on five chips. LaVell had 15 to 20 system engineers and there was another applications engineering group of similar size.

Tom Bennett had a background in industrial controls and had worked for Victor Comptometer
Victor Technology
Victor Technology LLC is a supplier of printing calculators, scientific calculators, financial calculators, basic calculators, and desktop accessories with headquarters in Bolingbrook, Illinois...

 in the 1960s designing the first electronic calculator to use MOS ICs, the Victor 3900. In May 1969 Ted Hoff showed Bennett early diagrams of the Intel 4004
Intel 4004
The Intel 4004 was a 4-bit central processing unit released by Intel Corporation in 1971. It was the first complete CPU on one chip, and also the first commercially available microprocessor...

 to see if it would meet their calculator needs. Bennett joined Motorola in 1971 to design calculator ICs. He was soon assigned as the chief architect of the microprocessor project that produced the 6800. Others have taken credit for designing the 6800. In September 1975 Robert Cushman, EDN magazine's microprocessor editor, interviewed Chuck Peddle about MOS Technology's new 6502
MOS Technology 6502
The MOS Technology 6502 is an 8-bit microprocessor that was designed by Chuck Peddle and Bill Mensch for MOS Technology in 1975. When it was introduced, it was the least expensive full-featured microprocessor on the market by a considerable margin, costing less than one-sixth the price of...

 microprocessor. Cushman then asked "Tom Bennett, master architect of the 6800," to comment about this new competitor. After the 6800 project Bennett worked on automotive applications and Motorola became a major supplier of microprocessors used in automobiles.

Jeff LaVell joined Motorola in 1966 and worked in the computer industry marketing organization. Jeff had previously worked for Collins Radio on their C8500 computer that was built with small scale ECL ICs. In 1971 he led a group that examined the needs of their existing customers such as: Hewlett Packard, National Cash Register, National Data Corporation (CDC), and Digital Equipment Corporation. They would study the customer's products and tried to identify functions that could be implemented in larger integrated circuits at a lower cost. The result of the survey was a family of 15 building bocks; each could be implemented in an integrated circuit. Some of these blocks were implemented in the initial M6800 release and more were added over the next few years. To evaluate the 6800 architecture while the chip was being designed, Jeff's team built an equivalent circuit using 451 small scale TTL ICs on five 10 by 10 inch (25 by 25 cm) circuit boards. Later they reduced this to 114 ICs on one board by using ROMs and MSI logic devices.

John Buchanan was a memory designer at Motorola when Bennett asked him to design a voltage doubler
Voltage doubler
A voltage doubler is an electronic circuit which charges capacitors from the input voltage and switches these charges in such a way that, in the ideal case, exactly twice the voltage is produced at the output as at its input....

 to for the 6800. Typical n-channel MOS IC's required three power supplies: -5 volts, +5 volts and +12 volts. The M6800 family was to use only one, +5 volts. It was easy to eliminate the -5 volt supply but the MOS transistors needed a supply of 10 to 12 volts. This on-chip voltage doubler would supply the higher voltage and Buchanan did the circuit design, analysis and layout for the 6800 microprocessor. He received patents on the voltage doubler and the 6800 chip layout. Rod Orgill assisted Buchanan with analyses and 6800 chip layout. Later Orgill would design the MOS Technology 6501 microprocessor that was socket compatible with the 6800.

Bill Lattin joined Motorola in 1969 and his group provided the computer simulation tools for characterizing the new MOS circuits in the 6800. Lattin and Frank Jenkins had both attended UC Berkley and studied computer circuit simulators under Donald Pederson
Donald Pederson
Donald O. Pederson was an American professor of electrical engineering at the University of California, Berkeley and one of the designers of SPICE, the canonical integrated circuit simulator.- Biography :...

, the designer of the SPICE
SPICE is a general-purpose, open source analog electronic circuit simulator.It is a powerful program that is used in integrated circuit and board-level design to check the integrity of circuit designs and to predict circuit behavior.- Introduction :Unlike board-level designs composed of discrete...

 circuit simulator. Motorola's simulator, MTIME, was an advanced version of the TIME circuit simulator that Jenkins had developed at Berkley. The group published a technical paper, "MOS-device modeling for computer implementation" in 1973 describing a "5-V single-supply n-channel technology" operating at 1 MHz. They could simulate a 50 MOSFET circuit on an IBM 370/165 mainframe computer. In November 1975, Lattin joined Intel to work on their next generation microprocessor.

Bill Mensch
Bill Mensch
American engineer William David Mensch, Jr., born 9 February 1945 in Quakertown, Pennsylvania, USA, is the founder, chairman and CEO of the Western Design Center of Mesa, Arizona...

 joined Motorola in 1971 after graduating from the University of Arizona. He had worked several years as an electronics technician before earning his BSEE degree. The first year at Motorola was a series of three month rotations through four different areas. Mensch did a flowchart for a modem that would become the 6860. He also worked the application group that was defining the M6800 system. After this training year, he was assigned to the 6820 Parallel Interface Adapter (PIA) development team. Mensch was a major contributor to the design of this chip and received a patent on the IC layout and was named as a co-inventor of seven other M6800 system patents. Later Mensch would design the MOS Technology 6502
MOS Technology 6502
The MOS Technology 6502 is an 8-bit microprocessor that was designed by Chuck Peddle and Bill Mensch for MOS Technology in 1975. When it was introduced, it was the least expensive full-featured microprocessor on the market by a considerable margin, costing less than one-sixth the price of...

Mike Wiles was a design engineer in Jeff LaVell's group and made numerous customer visits with Tom Bennett during 6800 product definition phase. He is listed as an inventor on eighteen 6800 patents but is best known for a computer program, MIKBUG. This was a rudimentary BIOS for a 6800 computer system that allowed the user to examine the contents of RAM and to save or load programs to tape. This 512 byte program occupied half of an MCM6830 ROM. This ROM was used in the Motorola MEK6800 design evaluation kit and early hobby computer kits. Wiles stayed with Motorola, moved to Austin and helped design the MC6801 microcontroller that was released in 1978.

Chuck Peddle
Chuck Peddle
Charles Ingerham Peddle is an American electrical engineer best known as the main designer of the MOS Technology 6502 microprocessor; the KIM-1 SBC; and its successor the Commodore PET personal computer, both based on the 6502....

 joined the design team in 1973 after the 6800 processor design was done but he contributed to overall system design and to several peripheral chips, particularly the 6820 (PIA) parallel interface. Peddle is listed as an inventor on sixteen Motorola patents, most have six or more co-inventors. Like the other engineers on the team, Peddle visited potential customers and solicited their feedback. Peddle and John Buchanan built one of the earliest 6800 demonstration boards. In August 1974 Chuck Peddle left Motorola and joined a small semiconductor company in Pennsylvania, MOS Technology
MOS Technology
MOS Technology, Inc., also known as CSG , was a semiconductor design and fabrication company based in Norristown, Pennsylvania, in the United States. It is most famous for its 6502 microprocessor, and various designs for Commodore International's range of home computers.-History:MOS Technology, Inc...

. There he led the team that designed the 6500 microprocessor family.

MC6800 microprocessor design

The Motorola 6800 and the Intel 8080 were designed at the same time and were similar in function. The 8080 was a superset of the Intel 8008 which was based on the Datapoint 2200
Datapoint 2200
The Datapoint 2200 was a mass-produced programmable terminal, designed by Phil Ray and Gus Roche, announced by Computer Terminal Corporation in June, 1970...

 processor. The 6800 architecture was modeled after the DEC PDP-11
The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...

 processor. Both are TTL compatible, have an 8-bit bidirectional data bus, a 16-bit stack pointer, a 16-bit address bus that can address 64 KB of memory and come in a 40-pin DIP
Dual in-line package
In microelectronics, a dual in-line package is an electronic device package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole mounted to a printed circuit board or inserted in a socket.A DIP is usually referred to as a DIPn, where n is...

 package. The 6800 has two accumulators and a 16-bit index register. The Direct Addressing mode allows fast access the first 256 bytes of memory. I/O devices are addressed as memory so there are no special I/O instructions. The 8080 has more internal registers and instructions for dedicated I/O ports. When the 8080 was reset, the program counter was cleared and the processor started at memory location 0000. The 6800 loaded the program counter from the highest address and started at the memory location stored there. The 6800 has a three-state control that will disable the address bus to allow another device direct memory access
Direct memory access
Direct memory access is a feature of modern computers that allows certain hardware subsystems within the computer to access system memory independently of the central processing unit ....

. A disk controller could transfer data into memory with no load on the processor. It is even possible to have two 6800 processors access the same memory.

MOS ICs typically used dual clock signals (a two-phase clock) in the 1970s. These were generated externally for both the 6800 and the 8080. The next generation of microprocessors incorporated the clock generation on chip. The 8080 had a 2 MHz clock but the processing throughput was similar to the 1 MHz 6800. The 8080 require more clock cycles to execute a processor instruction. The 6800 had a minimum clock rate of 100 kHz while the 8080 could be halted. Higher speed versions of both microprocessors were released by 1976.

Other divisions in Motorola developed components for the M6800 family. The Components Products Department designed the MC6870 two-phase clock IC; the Memory Products group provided a full line of ROMs and RAMs. The CMOS group's MC14411 Bit Rate Generator provided a 75 to 9600 baud clock for the MC6850 serial interface. The buffers for address and data buses were standard Motorola products. Motorola could supply every IC, transistor and diode necessary to build a MC6800 based computer.


The first generation metal-oxide semiconductors used p-channel field effect transistors, known as a p-channel MOSFET. (P-channel describes the configuration of the transistor.) These ICs were used in calculators and the first microprocessor, the Intel 4004. They were easy to produce but were slow and difficult to interface to the popular TTL digital logic ICs. An n-channel MOS integrated circuit could operate two or three times faster and was compatible with TTL. They were much more difficult to produce because of an increased sensitivity to contamination that required an ultra clean production line and meticulous process control. Motorola did not have an n-channel MOS production capability and had to develop one for the 6800 family.

Motorola's n-channel MOS test integrated circuits were complete in late 1971 and these indicated the clock rate would be limited to 1 MHz. These used "enhancement-mode" MOS transistors. There was a newer fabrication technology that used "depletion-mode" MOS transistors that would allow smaller and faster circuits. (This was also known as "depletion-load".) The "depletion-mode" processing required extra steps so Motorola decided to stay with "enhancement-mode" for the new single supply voltage design. The 1 MHz clock rate meant the chip designers would have to come up with several architectural innovations to speed up the microprocessor throughput. These resulting circuits were faster but required more area on the chip.

In the 1970s, semiconductors were fabricated on 3 inch (75 mm) diameter silicon wafers
Wafer (electronics)
A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices...

. Each wafer could produce 100 to 200 integrated circuit chips or dies. The technical literature would state the length and width of each chip in "mils" (0.001 inch). The Intel 8080 microprocessor chip size was 164 mils x 191 mils (4.1 mm by 4.9 mm). The current industry practice is to state the chip area so the size of the 8080 chip would be 19.7 mm2.

Processing wafers required multiple steps and flaws would appear at various locations on the wafer during each step. The larger the chip the more likely it would encounter a defect. The percentage of working chips or yield began to decline for chips larger than 160 mils (4 mm) on a side. The target size for the 6800 was 180 mils (4.6 mm) on each side but the final size was 212 mils (5.4 mm ) with an area of (29.0 mm2). At 180 mils, a 3 inches (76.2 mm) wafer will hold about 190 chips, 212 mils reduces that to 140 chips. At this size the yield may be 20% or 28 chips per wafer. The Motorola 1975 annual report highlights the new MC6800 microprocessor but has several paragraphs on the "MOS yield problems." The yield problem was solved with design revision started in 1975 to use depletion mode in the M6800 family devices. The 6800 die size was reduced to 160 mils (4 mm) per side with an area of 16.5 mm2. This also allowed faster clock speeds, the MC68A00 would operate at 1.5 MHZ and the MC68B00 at 2.0 MHz. The new parts were available in July 1976.

M6800 family introduction

The March 7, 1974 issue of Electronics had a two-page story on the Motorola MC6800 microprocessor along with the MC6820 peripheral interface adapter, the MC6850 communications interface adapter, the MCM6810 128 byte RAM and the MCM6830 1024 byte ROM. This was followed by an eight-page article in the April 18, 1974 issue authored by the Motorola design team. This issue also had an article introducing the Intel 8080

The Intel 8080 and the Motorola MC6800 processors both began layout around December 1972. The first working 8080 chips were produced January 1974 and the first public announcement was in February 1974. The 8080 used same three voltage N-channel MOS process as Intel's existing memory chips allowing full production to begin that April.

The first working MC6800 chips were produced in February 1974 and engineering samples were given to select customers. Hewlett Packard in Loveland, Colorado wanted the MC6800 for a new desktop calculator and had a prototype system working by June. The MC6800 used a new single voltage N-channel MOS process that proved to be very difficult to implement. The M6800 microcomputer system was finally in production by November 1974. Motorola matched Intel's price for single microprocessor, $360. (The IBM System/360 was a well-known computer at this time.)

Link Young was the product marketer that developed the total system approach for the M6800 family release. In addition to releasing a full set of support chips with the 6800 microprocessor, Motorola offered a software and hardware development system. The software development tools were available on remote time-sharing
Time-sharing is the sharing of a computing resource among many users by means of multiprogramming and multi-tasking. Its introduction in the 1960s, and emergence as the prominent model of computing in the 1970s, represents a major technological shift in the history of computing.By allowing a large...

 computers or the source code was available so the customer could use an in-house computer system. The software that would run on a microprocessor system was typically written in assembly language. The development system consisted of a text editor, assembler and a simulator. This allowed the developer to test the software before the target system was complete. The hardware development was a desktop computer build with M6800 family CPU and peripherals known as the EXORcisor. Motorola offered a three to five day microprocessor design course for the 6800 hardware and software. This systems-oriented approach became the standard way new microprocessor were introduced.

Design team break-up

The principal design effort on the M6800 family was complete in mid 1974 and many engineers left the group or the company. Several factors led to the break-up of the design group.

Motorola had opened a new MOS semiconductor facility in Austin Texas and entire engineer team was scheduled to relocate there in 1975. Many of the employees liked living in the Phoenix suburb of Mesa and were very wary about moving to Austin. The team leaders were unsuccessful with their pleas to senior management on deferring the move.

A recession hit the semiconductor industry in mid 1974 resulting in thousands of layoffs. A November 1974 issue of Electronics magazine reports that Motorola had laid off 4,500 employees, Texas Instruments 7000 and Signetics 4000. Motorola's Semiconductor Products Division would lose $30 million dollars in the next 12 months and there were rumors that the IC group would be sold off. Motorola did not sell the division but they did change the management and organization. By the end of 1974 Intel fired almost a third of its 3500 employees. The MOS IC business rebounded but job security was not taken for granted in 1974 and 1975.

Chuck Peddle (and other Motorola engineers) had been visiting customers to explain the benefits of microprocessors. Both Intel and Motorola had initially set the price of a single microprocessor at $360. Many customers were hesitant to adopt this new microprocessor technology with such a high price tag. (The actual price for production quantities was much lower.) In mid 1974 Peddle proposed a simplified microprocessor that could be sold at a much lower price. Motorola's "total product family" strategy did not focus on the price of MPU but on reducing the customer's total design cost. Their immediate goal was to get their completed system into production and they would work on improvements in 1975.
Peddle continued working for Motorola while looking for investors for his new microprocessor concept. In August 1974 Chuck Peddle left Motorola and joined a small semiconductor company in Pennsylvania, MOS Technology. He was followed by seven other Motorola engineers: Harry Bawcum, Ray Hirt, Terry Holdt, Mike James, Will Mathis, Bill Mensch and Rod Orgill. Peddle's group at MOS Technology developed two new microprocessors that were compatible with the Motorola peripheral chips like the 6820 PIA. Rod Orgill designed the MSC6501 processor that would plug into a MC6800 socket and Bill Mensch did the MSC6502 that had the clock generation circuit on chip. These microprocessors would not run 6800 programs because they had a different architecture and instruction set. The major goal was a microprocessor that would sell for under $25. This would be done by removing non-essential features to reduce the chip size. An 8-bit stack pointer was used instead of a 16-bit one. The second accumulator was omitted. The address buffers did not have a three-state mode for Direct Memory Access (DMA) data transfers. The goal was to get the chip size down to 153 mils x 168 mils (3.9 mm x 4.3 mm).

Chuck Peddle was a very effective spokesman and the MOS Technology microprocessors were extensively covered in the trade press. One of the earliest was a full-page story on the MCS6501 and MCS6502 microprocessors in the July 24, 1974 issue of Electronics magazine. Stories also ran in EE Times (August 24, 1975), EDN (September 20, 1975), Electronic News (November 3, 1975) and Byte (November 1975). Advertisements for the 6501 appeared in several publications the first week of August 1975. The 6501 would be for sale at the WESCON tradeshow in San Francisco, September 16–19 1975, for $25 each. In September 1975 the advertisements included both the 6501 and the 6502 microprocessors. The 6502 would only cost $20.

Motorola responded to MOS Technology's $20 microprocessor by immediately reducing the single unit price of the 6800 microprocessor from $175 to $69 and then suing MOS Technology in November 1975. Motorola claimed that the eight former Motorola engineers used technical information developed at Motorola in the design of the 6501 and 6502 microprocessors. MOS Technology's other business, calculator chips, was declining due to a price war with Texas Instruments so their financial backer, Allen-Bradley
Allen-Bradley is the brand-name of a line of Factory Automation Equipment manufactured by Rockwell Automation . The company, with revenues of approximately US$4.5 billion in 2006, manufactures programmable automation controllers , human-machine interfaces, sensors, safety components and systems,...

, decided to limit the possible losses and sold the assets of MOS Technology back to the founders. The lawsuit was settled in April 1976 with MOS Technology dropping the 6501 chip that would plug into a Motorola 6800 socket and licensing Motorola's peripheral chips. Motorola reduced the single unit price of the 6800 to $35.

The MOS Technology vs. Motorola lawsuit has developed a David and Goliath narrative over the years. One point was the Motorola did not have patents on the technology. This was technically true when the lawsuit was filed in late 1975. On October 30, 1974, before the 6800 was released, Motorola filed numerous patents applications on the microprocessor family and was granted over twenty patents. The first was to Tom Bennett on June 8, 1976 for the 6800 internal address bus. The second was to Bill Mensch on July 6, 1976 for the 6820 chip layout. Many of these patents named several of the departing engineers as co-inventors. These patents covered the 6800 bus and how the peripheral chips interfaced with the microprocessor.

Intel had a similar incident. Federico Faggin
Federico Faggin
Federico Faggin , who received in 2010 the National Medal of Technology and Innovation by Barack Obama, the highest honor bestowed by the United States government on scientists, engineers, and inventors, at the White House in Washington, is an Italian-born and naturalized U.S...

, who had led the development of the Intel's first microprocessor, the 4004, and it latest, the 8080, grew restless under the management changes at Intel. Faggin and another Intel engineer, Ralph Ungermann, began talking about starting up their own microprocessor company. Faggin and Ungermann left Intel and started Zilog
Zilog, Inc., previously known as ZiLOG , is a manufacturer of 8-bit and 24-bit microcontrollers, and is most famous for its Intel 8080-compatible Z80 series.-History:...

 in November 1974. Masatoshi Shima
Masatoshi Shima
is a Japanese electronics engineer, who was one of the designers of the world's first microprocessor, the Intel 4004, along with Federico Faggin, Ted Hoff, and Stanley Mazor....

, the designer of the Intel 8080, joined Zilog in February 1975 and they obtained funding from Exxon's venture capital group in June 1975. Zilog decided to make a superset of the Intel 8080 that also incorporated features from the 6800 and others. The Z80 only required a single 5 volt power supply and a single phase clock input. It was the first microprocessor to offer built-in support for dynamic RAM.

Move to Austin

Gary Daniels was designing ICs for electronic wristwatches when Motorola shutdown their Timepiece Electronics Unit. Tom Bennett offered him a job in the microprocessor group in November 1974. Bennett did not want to leave the Phoenix area so Gary Daniels managed the microprocessor development in Austin. (Daniels was the microprocessor design manager for the next ten years before he was promoted to a vice president.)

The first task was to redesign the 6800 MPU to make it more manufacturable and to operate at a faster clock. This design used depletion-mode technology and was know internally as the MC6800D. The transistor count went from 4000 to 5000 but the die area was reduced from 29.0 mm2 to 16.5 mm2. The maximum clock rate for selected parts doubled to 2 MHz. The other chips in the M6800 family were also redesigned to use depletion-mode technology. The Peripheral Interface Adapter had a slight change in the electrical characteristics of the I/O pins so the MC6820 became the MC6821. These new IC were completed in July 1976.

A new low cost clock generator chip, the MC6875, was released in 1977. It replaced the $35 MC6870 hybrid IC. The MC6875 came in a 16-pin dip package and could use quartz crystal or a resistor capacitor network.

Another project was incorporating 128 bytes of RAM and the clock generator on a single 11,000 transistors chip. The MC6802 microprocessor was released in March 1977. The companion MC6846 chip had 2048 byte ROM, an 8-bit bidirectional port and a programmable timer. This was a two chip microcomputer. The 6802 has an on-chip oscillator that uses an external 4 MHz quartz crystal to produce the two-phase 1 MHz clock. The internal 128 byte RAM could be disabled by grounding a pin and devices with defective RAM were sold as a MC6808.

A series of peripheral chip were introduced by 1978. The MC6840 Programmable Counter had three 16-bit binary counters that could be used for frequency measurement, event counting, or interval measurement. The MC6844 Direct Memory Access Controller could transfer data from an I/O controller to RAM without loading down the MC6800 microprocessor. The MC6845 CRT Controller provided the control logic for a character base computer terminal. The 6845 had support for a light pen
Light pen
A light pen is a computer input device in the form of a light-sensitive wand used in conjunction with a computer's CRT TV set or monitor. It allows the user to point to displayed objects, or draw on the screen, in a similar way to a touch screen but with greater positional accuracy...

, an alternative to a computer mouse. This was a very popular chip and was even used in the original IBM PC monochrome display card with the Intel 8088 16-bit microprocessor in 1981.

The MC6801 was a single chip microcomputer with a 6802 CPU with 128 bytes of RAM, a 2 KB ROM, a 16 bit timer, 31 programmable parallel I/O lines, and a serial port. It could also use the I/O lines as data and address buses to connect to standard M6800 peripherals. The 6801 would execute 6800 code but it had ten additional instructions and the execution time of key instructions was reduced. The two 8-bit accumulators could act as a single 16-bit accumulator for double precision addition, subtraction and multiplication. It was initially designed for automotive use with General Motors as the lead customer. The first application was a trip computer for the 1978 Cadillac Seville. This 35,000 transistor chip was too expensive for wide-scale adoption in automobiles so a reduced function MC6805 single chip microcomputer was designed.

The MC6809 was the most advanced 8-bit microprocessor Motorola produced. It had a new instruction set that was similar to the 6800 but abandoned op-code compatibility for improved performance and high-level language support; the two were software compatible in that assemblers could (and generally did) generate code which was equivalent to 6800 opcodes the 6809 did not directly emulate. In that sense, the 6809 was upward compatible with the 6800. The 6809 had many 16-bit operations, including the first 16-bit multiply instruction in a microprocessor, and two 16-bit index registers and stack pointers.

Personal computers

Micro Instrumentation and Telemetry Systems
Micro Instrumentation and Telemetry Systems was an American electronics company founded in Albuquerque, New Mexico that began manufacturing electronic calculators in 1971 and personal computers in 1975. Ed Roberts and Forrest Mims founded MITS in December 1969 to produce miniaturized telemetry...

 Altair 8800
Altair 8800
The MITS Altair 8800 was a microcomputer design from 1975 based on the Intel 8080 CPU and sold by mail order through advertisements in Popular Electronics, Radio-Electronics and other hobbyist magazines. The designers hoped to sell only a few hundred build-it-yourself kits to hobbyists, and were...

, the first successful personal computer, used the Intel 8080 microprocessor and was featured on the January 1975 cover of Popular Electronics. The first personal computers using the Motorola 6800 were introduced in late 1975. Sphere Corporation of Bountiful, Utah ran a quarter-page advertisement in the July 1975 issue of Radio-Electronics for a $650 computer kit with a 6800 microprocessor, 4 kilobytes of RAM, a video board and a keyboard. This would display 16 lines of 32 characters on a TV or monitor. The Sphere computer kits began shipping in November 1975. Southwest Technical Products Corporation
The U.S. company SWTPC started in 1964 as DEMCO . It was incorporated in 1967 as Southwest Technical Products Corporation of San Antonio, Texas...

 of San Antonio, Texas, officially announced their SWTPC 6800 Computer System in November 1975. Wayne Green
Wayne Green
Wayne Green is an American publisher and writer, and consultant. He was formerly editor of CQ magazine before he went on to found 73, 80 Micro, Byte, CD Review, Cold Fusion, Kilobaud Microcomputing, RUN , InCider, and Pico, as well as publishing books and running a software company...

 visited SWTPC in August 1975 and described the SWTPC computer kit complete with photos of a working system in the October 1975 issue of 73
73 (magazine)
73 Magazine was a United States-based amateur radio magazine that was published from 1960 to 2003. It was known for its strong emphasis on technical articles and for the lengthy editorials in each issue by its founder and publisher, Wayne Green...

. The SWTPC 6800 was based on the Motorola MEK6800 design evaluation kit chip set and used the MIKBUG ROM Software. The MITS Altair 680 was on the cover of the November 1975 issue of Popular Electronics. The Altair 680 used a 6800 microprocessor and also had a front panel with toggle switches and LEDs. The initial design had to be revised and first deliveries of the Altair 680B were in April 1976.

Sphere was a small startup company and had difficulties delivering all of the products they announced. They filed for a Chapter 11 bankruptcy in April 1977. The Altair 680B was popular but MITS focused most of the resources on their Altair 8800 computer system and they exited the hobby market in 1978. The Southwest Technical Products computer was the most successful 6800 based personal computer. Other companies, for instance, Smoke signal Broadcasting (California), Gimix (Chicago), Midwest Scientific (Olathe, Kansas), and Helix Systems (Hazelwood, Missouri), started producing SWTPC 6800 compatible boards and complete systems. The 8080 systems were far more popular than the 6800 ones.
The Tektronix 4051
Tektronix 405x
The Tektronix 405x series was a series of graphics microcomputers produced by Tektronix in the late 1970s through the early 1980s. The display technology was similar to the Tektronix 4014 terminal, using a storage tube display to avoid the need for video RAM...

 Graphics Computing System was introduced in October 1975. This was a professional desktop computer that had a 6800 microprocessor with up to 32 kb of user RAM, 300 kb magnetic tape storage, BASIC in ROM and a 1024 by 780 graphics display. The Tektronix 4051 sold for $7000, rather higher than the personal computers using the 6800.

By 1977 personal computers were fully assembled and ready to use, not do-it-yourself kits. The Apple II
Apple II series
The Apple II series is a set of 8-bit home computers, one of the first highly successful mass-produced microcomputer products, designed primarily by Steve Wozniak, manufactured by Apple Computer and introduced in 1977 with the original Apple II...

 and Commodore PET
Commodore PET
The Commodore PET was a home/personal computer produced from 1977 by Commodore International...

 were based on the MOS Technology 6502 microprocessor designed by former Motorola engineers. The Radio Shack TRS-80
TRS-80 was Tandy Corporation's desktop microcomputer model line, sold through Tandy's Radio Shack stores in the late 1970s and early 1980s. The first units, ordered unseen, were delivered in November 1977, and rolled out to the stores the third week of December. The line won popularity with...

 used the Zilog Z80
Zilog Z80
The Zilog Z80 is an 8-bit microprocessor designed by Zilog and sold from July 1976 onwards. It was widely used both in desktop and embedded computer designs as well as for military purposes...

 microprocessor designed by former Intel engineers, Federico Faggin and Masatoshi Shima.

The architecture and instruction set of the 6800 were easy for beginners to understand and Heathkit
Heathkits were products of the Heath Company, Benton Harbor, Michigan. Their products included electronic test equipment, high fidelity home audio equipment, television receivers, amateur radio equipment, electronic ignition conversion modules for early model cars with point style ignitions, and...

 developed a microprocessor course and the ET3400 6800 trainer. The course and trainer proved popular with individuals and schools.

Motorola's next generation 8-bit microprocessor architecture, the MC6809
Motorola 6809
The Motorola 6809 is an 8-bit microprocessor CPU from Motorola, designed by Terry Ritter and Joel Boney and introduced 1978...

 (1979), was used in the Radio Shack TRS-80 Color Computer
TRS-80 Color Computer
The Radio Shack TRS-80 Color Computer was a home computer launched in 1980. It was one of the earliest of the first generation of computers marketed for home use in English-speaking markets...

 and the compatible Dragon 32/64
Dragon 32/64
The Dragon 32 and Dragon 64 are home computers that were built in the 1980s. The Dragons are very similar to the TRS-80 Color Computer , and were produced for the European market by Dragon Data, Ltd., in Port Talbot, Wales, and for the US market by Tano of New Orleans, Louisiana...

 which was sold in Europe. SWTPC also released a 6809 based system, the s/09, as did other SS-50 vendors. The 6809 and the 16/32 bit 68000
Motorola 68000
The Motorola 68000 is a 16/32-bit CISC microprocessor core designed and marketed by Freescale Semiconductor...

 were incompatible with the instruction set of the 6800, but could use 6800-family peripheral chips.


List from "Motorola Microcomputer Components", November 1978
Part Description Image
MC6810 128 byte static RAM Brochure
MC6820 Peripheral Interface Adapter
Peripheral Interface Adapter
The Peripheral Interface Adapter is a peripheral integrated circuit providing parallel I/O interfacing capability for microprocessor systems. Common PIAs include the Motorola MC6820 and MC6821, and the MOS Technology MCS6520, all of which are functionally identical but have slightly different...

MC6821 Peripheral Interface Adapter (PIA) Brochure
MC6828 Priority Interrupt Controller (PIC) Brochure
MCM6830 1024 byte ROM Brochure
MC6840 Programmable Timer Module (PTM) Brochure
MC6843 Floppy Disk Controller (FDC) Brochure
MC6844 Direct Memory Access Controller (DMAC) Brochure
MC6845  CRT Controller (CRTC) Brochure
MC6846 ROM-I/O-Timer Brochure
MC68488 General Purpose Interface Adapter (GPIB) IEEE488 Brochure
MC6850 Asynchronous Communication Interface Adapter (ACIA) Brochure
MC6852 Synchronous Serial Data Adapter (SDAA) Brochure
MC6854 Advanced Data Link Controller (ADLC) Brochure
MC6860 0-600 bit/s Digital Modem Brochure
MC6862 2400 bit/s Modulator Brochure
MC6870 Two Phase Microprocessor Clock Advertisement
MC6875 Clock Generator Brochure

Second sources

A common requirement for manufacturing companies was to require two or more sources for every part in the products they made. This ensured they could get parts if a supplier had financial problems or a disaster. Initially Motorola selected American Microsystems Inc (AMI) as a second source for the M6800 family. Hitachi, Fujitsu, Fairchild, Rockwell and Thomson Semiconductors were added later.

Oral histories

External links