Zilog z80 processor: The Z80 Microprocessor

Marcian E. «Ted» Hoff

The Busicom engineers had no interest in dumping their design in favor of Hoff’s unproved proposal. But Hoff, with Noyce’s blessing, started working on the project. Soon Mazor, then a research engineer at Intel, joined him, and the two pursued Hoff’s ideas, developing a simple instruction set that could be implemented with about 2000 transistors. They showed that the one set of instructions could handle decimal addition, scan a keyboard, maintain a display, and perform other functions that were allocated to separate chips in the Busicom design.

In October 1969, Hoff, Mazor, and the three Japanese engineers met with Busicom management, visiting from Japan, and described their divergent approaches. Busicom’s managers chose Hoff’s approach, partly, Hoff said, because they understood that the chip could have varied applications beyond that of a calculator. The project was given the internal moniker “4004.”

Federico Faggin, now president and chief executive officer of Synaptics Inc., San Jose, Calif., was assigned to design the chip, and in nine months came up with working prototypes of a 4-bit, 2300-transistor “microprogrammable computer on a chip.” Busicom received its first shipment of the devices in February 1971.

Faggin recalled that when he began implementing the microprocessor, Hoff seemed to have lost interest in the project, and rarely interacted with him. Hoff was already working on his next project, the preliminary design of an 8-bit microprogrammable computer for Computer Terminals Corp., San Antonio, Texas, which, architected by Computer Terminals, was named the 8008. Hoff always “had to do very cutting-edge work,” Faggin told Spectrum. “I could see a tension in him to always be at the forefront of what was happening. ”

In those early Intel days, Mazor recalled that Hoff had a number of ideas for projects, many of which, though not commercially successful, proved prescient: a RAM chip that would act like a digital camera and capture an image in memory, a video game with moving spaceships, a device for programming erasable programmable ROMs, and computer-aided design tools intended for logic simulation.

The Intel marketing department they estimated that sales [of microprocessors] might total only 2000 chips a year.

Meanwhile, the microprocessor revolution was gearing up, albeit slowly. Hoff joined Faggin as a microprocessor evangelist, trying to convince people that general-purpose one chip computers made sense. Hoff said his toughest sell was to the Intel marketing department.

“They were rather hostile to the idea,” he recalled, for several reasons. First, they felt that all the chips Intel could make would go for several years to one company, so there was little point in marketing them to others. Second, they told Hoff, ‘‘We have diode salesman out there struggling like crazy to sell memories, and you want them to sell computers? You’re crazy.” And finally, they estimated that sales might total only 2000 chips a year.

But word went out. In May 1971 an article in Datamation magazine mentioned the product, and the following November Intel produced its first ad for the 4004 CPU and placed it in Electronic News. By 1972 stories about the miracle of what began being called the microprocessor started appearing regularly in the press, and Intel’s competitors followed its lead by launching microprocessor products of their own.

Hoff never even considered patenting the microprocessor. To him the invention seemed to be obvious.

One step Hoff did not take at that time was apply for a patent, even though he had already successfully patented several inventions. (Later, with Mazor and Faggin he filed for and was granted a patent for a “memory system for a multi-chip digital computer. ”)

Looking back, Hoff recalled that he never even considered patenting the microprocessor in those days. To him the invention seemed to be obvious, and obviousness was considered grounds for rejecting a patent application (though, Hoff said bitterly, the patent office currently seems to ignore that rule). It was obvious to Hoff that if in one year a computer could be built with 1000 circuits on100 chips, and if in the following year those 1000 circuits could be put onto10 chips, eventually those 1000 circuits could be con­ structed on one chip.

Instead of patenting, Hoff in March 1970 published an article in the proceedings of the 1970 IEEE International Convention that stated: “An entirely new approach to design of very small computers is made possible by the vast circuit complexity possible with MOS technology. With from 1000 to 6000 MOS devices per chip, an entire central processor may be fabricated on a single chip.”

But in December 1970, an independent inventor outside the cliquish semiconductor industry, Gilbert Hyatt, filed for a patent on a processor and mentioned that it was to be made on a single chip. In 1990, after numerous appeals and extensions, Hyatt was granted that patent and began collecting royalties from many microprocessor manufacturers. Currently, though history traces today’s microprocessor back to Hoff, Mazor, and Faggin, the legal rights to the invention belong to Hyatt.

The Invention of the Codec

While the microprocessor has proved to be his most celebrated achievement, Hoff does not view it as his biggest technical breakthrough. That designation he reserves for the single-chip analog-to-digital/ digital-to-analog coder/decoder (codec).

“Now that work was an exciting technical challenge,” Hoff recollected with some glee, “because there were so many who said it couldn’t be done.”

The project was kicked off by Noyce, who spotted the telephone industry as ripe for new technology, and urged Hoff to find an important product for that market. Studying telephone communications, Hoff and several other researchers saw that digitized voice transmission, then being used between central offices, depended on the use of complex expensive codecs that tied into electromechanical switches.

”We thought,” Hoff told Spectrum, “we could integrate this, the analog-to-digital conversion, on a chip, and then use these circuits as the basis for switching.”

Besides reducing the cost of the systems to the telephone company, such chips would enable companies to build small branch exchanges that handled switching electronically.

Hoff and his group developed a multiplexed approach to conversion in which a single converter is shared by the transmit and receive channels. They also established a number of other techniques for conversion and decoding that Hoff saw as not being obvious and for which he received patents.

With that project’s completion in 1980, after six years of effort, and its transfer to Intel’s manufacturing facility in Chandler, Ariz., Hoff became an Intel Fellow, free to pursue whatever technology interested him. What interested him was returning to his work on adaptive structures, combining the concepts he had wrestled with at Stanford with the power of the microprocessor in the service of speech recognition. After a year he built a recognition system that Intel marketed for several years.

A prime customer for the system was the automotive industry. Its inspectors used the systems to help them check out a car as it finally left the assembly line. When an inspector noted out loud various problems that needed fixing, the system would prompt him for further information, and log his responses in a computer.

From Intel to Atari

Though his position as an Intel Fellow gave Hoff a fair amount of freedom, he found himself getting bored. Intel’s success in microprocessors by 1983 had turned it into a chip supplier, and other companies were designing the chips into systems.

“I had always been more interested in systems than in chips,” Hoff said, “and I had been at Intel for 14 years, at a time when the average stay at a company in Silicon Valley was three years. I was overdue for a move.”

Again, Hoff had not gone beyond thinking about leaving Intel when a new job came to him. Atari Inc., Sunnyvale, Calif., then a booming video game company owned by Warner Communications Inc. and a major user of microprocessors, was looking for a vice president of corporate technology. In February 1983, after discussing the scope of the ideas that Atari researchers were pursuing, Hoff latched onto the opportunity.

Intel from the start had a structured, highly controlled culture. At Atari, chaos reigned.

Intel from the start had a structured, highly controlled culture. At Atari, chaos reigned. Under Hoff were research laboratories in Sunnyvale, Los Angeles, and Grass Valley, Calif.; Cambridge, Mass.; and New York City. Researchers were working on picture telephones, electronic aids for joggers, computer controls that gave tactile feedback, graphical environments akin to today’s virtual reality, digital sound synthesis, advanced personal computers, and software distribution via FM sidebands.

But Hoff had barely had time to learn about all the research projects under way before the video game business took a well-publicized plunge. Without solid internal controls, Atari was unable to determine how well its games were selling at the retail point, and distributors were returning hundreds of thousands of cartridges and game machines. Hoff began receiving orders for staff cuts monthly.

“It would have been one thing if I had known I had to cut back to, say, one-quarter the size of my group,” he told Spectrum. “But when every month you find you have to cut another chunk, morale really drops.”

In July 1984, while Hoff was at his 30th high school reunion, Warner sold Atari to Jack Tramiel. Hoff then had to choose between convincing Tramiel that he could play a role in a narrowly focused company uninterested in funding futuristic research, and allowing Warner to buy out his contract. He chose the latter.

Looking back, most of the people who were at Atari in those days now view them darkly. But Hoff recalls his year there as an enjoyable and ultimately useful experience. “Maybe I look at it more positively than I should,” he said, “but it turned out to be a good transition for me, and the life I have now is a very nice one. ”

“Whenever you are working on one problem, there is always another problem over here that seems more interesting.”
—Hoff

He now spends half his time as a consultant and half pursuing technical projects of his own devising—a read­out device for machine tools, various types of frame grabbers, pattern recognition, and techniques for analog-to-digital conversion. This variegated schedule is perfect for him. He has always felt himself to be a generalist, and has had trouble focusing on just one technology.

“It’s easy for me to get distracted,” he said. “Whenever you are working on one problem, there is always another problem over here that seems more interesting. But now it is more likely that my own projects get delayed, rather than things critical to other people and their employment.”

Faggin for one is not surprised that such independent work appeals to Hoff. “He never was the gregarious type,” Faggin said. “He liked introverted work, the thinking, the figuring out of new things. That is what he is good at. I always was impressed how he was able to visualize an architecture for a new IC, practically on the spot.”

“He comes up with idea after idea, situation after situation. I think if he wanted to, Ted could sit down and crank out a patent a month.”
—Gary Summers

Said Gary Summers, president and chief executive officer of Teklicon Inc., Mountain View, the consulting firm that employs Hoff today: “He comes up with idea after idea, situation after situation. I think if he wanted to, Ted could sit down and crank out a patent a month.”

“There is no doubt in my mind that he is a genius,” Mazor stated. Summers readily concurred.

Hoff’s first project after Atari was a voice­controlled music synthesizer, which gave off the sound of a selected instrument when someone sang into it. Hoff’s biggest contribution to the project was a system that ensured that the emerging notes would be in tune, or at least harmonically complement the tune, even when the singer strayed off key. He scored another patent for this system, and the gadget was sold briefly through the Sharper Image catalog, but never became a big success.

Hoff still contributes occasionally to product designs. At Teklicon, however, where he is vice president and chief technical officer, most of his consulting is done for lawyers. Hoff has a unique combination of long experience with electronic design and long-standing pack rat habits. His home workshop contains about eight personal computers of different makes and vintages, five oscilloscopes, including a vintage Tektronix 545 scope, 15000 ICs inventoried and filed, and shelves loaded with IC data books dating right back to the 1960s.

“If my washing machine breaks down, I call the repairman. Most clever engineers would buy the replacement gear and install it. Ted is capable of analyzing the reason the gear failed in the first place, redesigning a better gear from basic principles, carving it out of wood, casting it at his home, and dynamically balancing it on his lathe before installing it. ”
—Mazor

When a lawyer shows him a patent disclosure, even one decades old, he can determine whether or not it could then have been “reduced to practice” and whether it provided sufficient information to allow “one of ordinary skill in the art” to practice the invention. Then he can build a model proving his conclusion, using vintage components from his collection, and demonstrate the model in court as an expert witness. This model-building can get very basic. On Spectrum’s visit, Rochelle salt crystals that Hoff attempted to grow for a recent court demonstration littered his workshop floor, next to metal-working equipment that he uses to build cases for his models.

Hoff sees this ability to get down to basics as one of his strengths. “I relate things to fundamental principles,” he said. “People who don’t question the assumptions made going into a problem often end up solving the wrong problem.”

Mazor said, “If my washing machine breaks down, I call the repairman. Most clever engineers would buy the replacement gear and install it. Ted is capable of analyzing the reason the gear failed in the first place, redesigning a better gear from basic principles, carving it out of wood, casting it at his home, and dynamically balancing it on his lathe before installing it.”

Doing legal detective work appeals to Hoff for another reason: it gives him an excuse to hunt for interesting “antique” components at flea markets and electronics stores.

Hoff cannot discuss the specifics of patent cases he has been involved with. Several recently were in the video game area; others have involved various IC companies. In a number of cases, Hoff was confident that his side was right, and his side still lost, so he felt little surprise when the microprocessor patent was granted to Hyatt. (After the award was made, though, he did sit down with Hyatt’s patent application and attempted to design a working microprocessor based on Hyatt’s disclosures. He found several incongruities—like a clock rate only suited to bipolar technology with logic that could only be rendered in MOS technology, and logic that required far too many transistors to put on a chip, proving in his mind that the award was incorrect. )

Seeing someone else get credit for the microprocessor, particularly in recent media reports, “is irritating,” Hoff told Spectrum, “but I’m not going to let it bother me, because I know what I did, I know what all the other people on our project did, and I know what kind of company Intel is. And I know that I was where the action was.”

Editor’s note: Hoff retired from Teklicon in 2007. He currently serves as a judge for the Collegiate Inventors Competition, held annually by the National Inventors Hall of Fame. These days, his main technical interests surround energy, water, and climate change.

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Zilog Z-80 — The Immortal of the Eighties / Sudo Null IT News instantly overgrown with many compatible analogues — both more affordable and more advanced, technically interesting. But long before companies crossed swords for buyers of the original 186 and their successors, competition also touched the first key chip in the history of the computer industry — the Intel 8080.

Intel 8080

The release of the Intel 8080 processor has become a catalyst for the development of the development and production of microprocessors that have found application in a variety of fields and areas. The release of various 8-bit solutions (such as Motorola 6800 or MOS Technologies 6502), as well as the production of fully compatible clone solutions (manufactured, in particular, by AMD), determined the needs of the market in the mid-70s, which can partly be called and the cause of the Z-80.

After leaving Intel, Federico Fagin and Ralph Ungermann began discussing what products they could develop. Ungermann was attracted by the idea of ​​creating electronic typewriters. And Fagin wanted to use the concept of the original 4004 microprocessor in a single-chip microcontroller that would contain all the memory and I / O devices with a processor on a single silicon element.

Federico Fagin (left) and Ralf Ungermann

Rumors about this reached the journalists from Electronics News, and in the next issue of the commercial magazine there was a large article that Fagin and Ungermann were going to go into the processor business together.

A week later, an unexpected visitor came to the office they rented in the prestigious area of ​​Los Altos, a few miles from Palo Alto. He introduced himself as an employee of a subsidiary of Exxon, the world’s largest oil company founded to invest in start-up companies. Exxon Enterprises, as his company was called, became interested in Fagin and Ungermann. If they want to develop a new microprocessor, the firm could support them.

The deal was closed quickly. The company received a controlling stake of 51% in exchange for $1.5 million.

Ungermann came up with a good name for the new business — «Zilog». This meant that the company considered itself «the last word [Z] in integral [I] logic [LOG]».

Two months later, Fagin had another idea. He followed the fate of his old project, the Intel 8080 processor. From the rave reviews in the commercial press, from the fact that companies across America were starting to use it, Fagin realized that it would be foolish not to capitalize on the wave of general-purpose microprocessor boom. December 19For 74 years, he convinced Ungermann to leave the controller project and switch to developing an improved version of the 8080 chip.

In an attempt to reconnect with Andy Grove, Faggin came to Intel with his ideas and offered to organize the production of an improved 8080 under a contract with Intel. However, his proposals were rejected.

Fajin was later approached by Masatoshi Shima, an engineer who oversaw the 4004 project and then moved to Intel, to apply for a job. Since Seema was developing the detailed blueprint for the 8080, Faggin was happy to invite him.

Masatoshi Shima

The new Zilog chip was built faster than Fajin and Ungermann expected. Working 80 hours a week on the chip, Fagin completed the architecture in less than nine months.
At first, Zilog united only three of them, they were assisted by several draftsmen, so the question of their own production of the chip was not raised. Faggin drew the drawing on graph paper with a stylus; Sima followed the creation of templates according to the drawings. The finished set of templates was sent for production to Mostek, a spin-off from Texas Instruments, which at that time was one of Intel’s strongest competitors in the MOS technology market. By March 1976 years Zilog got a working device capable of conquering the world.

The Z-80 is a third generation single-chip microprocessor with 8-bit data and 16-bit addresses. It contained 8500 transistors and was produced according to 3-micron process standards. The area of ​​the crystal was 22.54 mm ² .
The maximum amount of directly addressable memory and directly addressable I/O space is 64 KB each (the I/O space of the 8080 microprocessor is 256 bytes).

Zilog Z-80

The Z80 microprocessor instruction set includes 158 instructions, 78 of which are completely similar to the 8080 microprocessor instructions, although they have different mnemonics. In addition to the arithmetic logic instructions traditional for 8-bit microprocessors, the Z80 has instructions that work with individual bits, and also facilitate the processing of character information.

Microprocessors were produced with various operating clock frequencies from 2.5 to 8 MHz (for 8080A — 2.5 MHz), which provided very high speed for those times.
Finally, a dynamic memory regeneration counter is implemented on the microprocessor chip itself, which makes it possible to drastically reduce the number of parts in simple microcomputers compared to 8080.

The Z-80 microprocessor was produced in a 40-pin DIP package, the most common for eight-bit microprocessors. Unlike the Intel 8080 microprocessor, the Z-80 does not require specific additional circuits (two-phase clock generator and system controller) for its operation, which greatly simplifies the design of the processor module. In addition, the Z80 requires a single supply voltage of +5 V to operate, instead of three voltages for the 8080 (+5, -5 and +12 V).

At only $200, the Z-80 also appealed to individual consumers who used to spend long nights at the amateur radio and now tinker with electronics, thanks to the triumph of large-scale circuit integration. The Z-80 allowed them to think for the first time about building a computer themselves. There were fewer computers in the world in 1974 than there were airplanes in 1997. So assembling a computer at the time was about the same as building a Boeing 767 in the backyard today. However, it wasn’t much scarier.

Having spent $400,000 to develop its chip, Zilog could not afford to pay generously for an army of sales agents. Instead, the company bought a seat in Electronic News magazine and published a series of promotional articles.

Due to the spread of the Z80 around the world, Zilog has been awarded many contracts for the production of its microprocessors in various parts of the world. After entering the market in 1976, the main partners in the United States were Synertek and Mostek, which produced the first series of Z-80 processors (at the end of 1976, Zilog opened its own factories, and provided the American market with the Z80 on its own). In Japan, the production of Z80 launched companies such as Toshiba and Hitachi. Due to the incredible popularity and demand for the Z80, many analogue manufacturers operated without a license, so in total less than half of all Z-80s produced turned out to be licensed products from Zilog or its official partners.

In our country, the Z80 is known primarily for the Sinclair Spectrum gaming computer, extremely popular in the second half of the 1980s.

Sinclair ZX Spectrum

However, the scope of this microprocessor was much wider. In particular, it is he who is the “brain” of the French Exocet anti-ship missiles (in 1982, the Argentine Mirage fighter sank the English destroyer Sheffield, one of the most modern warships at that time, with such a missile).

The Zilog Z80 processor not only became incredibly popular after entering the market, but also proved to be a long-lived record holder — for decades it has been present in various systems as one of the specialized microprocessors, used in computer, portable, and business systems of the most different levels and purposes. In the 80s, it became part of portable systems such as Sharp PC-1500 and Cambridge Z88, at 90-e began to be used in engineering calculators of the TI-81 family from Texas Instruments.

TI-81

It was also used as a musical instrument microprocessor (eg the legendary Prophet-5 MIDI keyboard), and many embedded systems still include the legendary microprocessor as part of their solutions.

Prophet-5

More than 40 years after its introduction on the market, the Zilog Z80 has been and remains indispensable in dozens of different computer systems, and can serve as an example of how computer technology, which appeared at the dawn of the personal computer era, are still part of our daily lives.

Our video based on the article — TYK

The author of the article is Alexander Lis.

Zilog Z80 CPU Test Suite • ZX Spectrum

Language

• Russian
• English

Control

• Keyboard(?)

Players

• One

• Description
• Description (EN)
• Information

Welcome to the Zilog Z80 CPU test suite.

This set of programs is designed to help emulator authors achieve the required level of Z80 emulation accuracy. Each of the included programs performs exhaustive calculations using each of the tested Z80 instructions, compares the result with the values ​​obtained on a real 48K Spectrum with a Zilog Z80 onboard, and reports any deviations found.

The following options are available:

— z80full — tests all flags and registers.
— z80doc — tests all registers, but only officially documented flags.
— z80flags — tests all flags, ignoring registers.
— z80docflags — only tests documented flags, ignores case.
— z80ccf — Tests all flags after executing CCF after each tested instruction.
— z80memptr — tests all flags after executing BIT N,(HL) after each tested instruction.

The first four are standard CPU emulation tests. The CCF variant is used to carefully test the true behavior of the SCF/CCF after each Z80 instruction. Finally, the MEMPTR variant can be used to detect problems in the MEMPTR emulation — however, note that the current test suite was not specifically designed for the MEMPTR stress test, so many of the possible problems are likely to go undetected. Eventually, I may add custom MEMPTR tests in recent releases.

Enjoy!

Patrik Rak

Official page and updates: https://github.com/raxoft/z80test

Welcome to the Zilog Z80 CPU test suite.

This set of programs is intended to help the emulator authors to reach the
desired level of the CPU emulation authenticity. Each of the included programs
performs an exhaustive computation using each of the tested Z80 instructions,
compares the results with values ​​obtained from a real 48K Spectrum with Zilog Z80 CPU,
and reports any deviations detected.

The following variants are available:

– z80full – tests all flags and registers.
— z80doc — tests all registers, but only officially documented flags.
— z80flags — tests all flags, ignores registers.
— z80docflags — tests documented flags only, ignores registers.
— z80ccf — tests all flags after executing CCF after each instruction tested.
— z80memptr — tests all flags after executing BIT N,(HL) after each instruction tested.

The first four are the standard tests for CPU emulation. The CCF variant is
used to thoroughly test the authentic SCF/CCF behavior after each Z80
instruction. Finally the MEMPTR variant can be used to discover problems in
the MEMPTR emulation – however note that the current set of test was not
specifically designed to stress test MEMPTR, so many of the possible
problems are very likely left undetected. I may eventually add specific
MEMPTR tests in later releases.

Enjoy!

Patrik Rak

Official download and updates: https://github.com/raxoft/z80test

The Zilog Z80 CPU Test Suite game runs directly on the site. This is a programming application published in the Czech Republic in 2012 by the Raxoft creative team, written by Patrik Rak.

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