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A History of Early Microcontrollers, Part 7: The Zilog Z8

When Federico Faggin arrived at Intel in 1970, he immediately discovered that he’d stepped into a royal mess. He’d left Fairchild Semiconductor and accepted the position at Intel before being fully briefed on the custom chip set project for Busicom that would eventually become the first commercially successful microprocessor, the 4004. Faggin had developed a silicon-gate MOS process technology at Fairchild, knew it was vastly superior to the metal-gate technology everyone was using at the time, and had inferred that Intel planned to use silicon-gate technology from watching some of the thirty or so people who’d already left Fairchild to follow Bob Noyce and Gordon Moore to their new semiconductor startup, Intel. Faggin wanted in as well, because Fairchild was ignoring his new process technology, so he called his old Fairchild boss Les Vadasz, now at Intel, and asked for a position. Vadasz quickly said yes.

The day that Faggin joined Intel on April 3, 1970, Stan Mazor handed him all the documentation on the Busicom project. Ted Hoff and Mazor had developed the high-level architecture and instruction set for the 4004 microprocessor, which left only the logic design, circuit design, and silicon-gate process development to be done. In other words, most of the project remained undone. In addition, Mazor informed Faggin that Masatoshi Shima, the Busicom engineer overseeing the project on the client side, was arriving from Japan the very next day for a progress report.

When Shima arrived the next day, he was so eager to check on the progress that he asked to be taken to Intel immediately to see the documentation. He wanted to see the progress on the logic design of the chips. There was no progress and Shima became quite angry. Faggin was able to calm Shima down, and then Shima called Busicom in Tokyo. The entire project was in jeopardy because there’d been no progress on the project over the past several months.

Welcome to Intel, Dr. Faggin.

From those shaky beginnings, Faggin managed the development of the Intel 4004, 4040, 8008, and 8080 microprocessors. By 1974, he was very probably the world’s foremost expert on the practice of microprocessor development, from architecture and instruction set all the way down to process technology. He was also ready to leave Intel. Bob Noyce and Gordon Moore were giving more and more day-to-day control of the company to Andy Grove, and his confrontational management style frustrated Faggin. In addition, Intel was riding the huge DRAM wave at the time and Grove was not particularly interested in microprocessors at that time. He considered them a distraction.

Then Faggin discovered that Intel had patented Faggin’s buried contact for the silicon-gate process, which Faggin had invented but not patented at Fairchild. Worse, Intel had done this without Faggin’s knowledge and had put the patent in the name of Faggin’s boss, Vadasz. The discovery of that act seems to have been the final straw for Faggin, who perpetually felt underappreciated by management at Intel and thought he’d been grossly undercompensated for his massive contributions to the company’s microprocessor programs.

By the late summer of 1974, Faggin decided to leave Intel and start his own company. He invited Ralph Ungerman, one of the managers who reported to him at Intel, out for a drink. Ungerman had taken over Intel’s microprocessor business from Faggin in early 1974. Faggin asked, “Ralph, how about starting a company – a microprocessor company – you and I?” Ungerman replied, “Okay!”, and that was the start of Zilog.

Faggin’s last day at Intel was October 31, 1974 – Halloween. He wanted to make a clean break with Intel, so he’d developed no business plan and had not arranged for funding. He just had the idea to start a microprocessor company and the first product he wanted to develop was a microcontroller. He called it the 2001. Ungerman had started a consulting business – Ungerman Associates – on the side while at Intel. When they became partners, Faggin bought half of that business. Ungerman’s consulting revenue initially funded the new company, eventually named Zilog.

Faggin developed the architecture and instruction set for the 2001 microcontroller during November and December. During that time, the leading trade newspaper of the day, Electronic News, ran an article about Faggin’s new microprocessor venture. That article caught the attention of a partner at Exxon Enterprises, the oil company’s investment operation. Faggin got a phone call from Exxon with a request to meet in a couple of days. Faggin agreed, had his wife type up a short business plan, and then the meeting occurred. Faggin presented the plan and his initial ideas for the 2001 microcontroller. The Exxon Enterprises partner said he was sufficiently interested to continue talking.

Then, in December, Faggin realized that the microcontroller business was not yet big enough to serve as the foundation for his new microprocessor company. The right product came to him in a flash on a Saturday in December, 1974. “Super-80!” he exclaimed. The vision he’d had was for a Super-80 microprocessor, based on the Intel 8080 architecture, but with numerous improvements such as twice as many registers, more instructions, more addressing modes, more bit-level instructions, and a better interrupt structure, and with peripheral chips designed as a family from the outset. Further, the Super-80 would be built using an NMOS process that required only a 5-volt power supply, so it would be far easier for system designers to use it. The Super-80 microprocessor would have an immediate and much larger target market than would the 2001 microcontroller.

Faggin called the investment partner at Exxon and informed him of his change in strategic direction. Exxon bought into the idea, and, by April of the next year, Faggin snagged a verbal commitment for a $500,000 investment from Exxon Enterprises. The 2001 microcontroller idea was shelved, and work began on the Super-80. Of course, the Super-80 became the incredibly successful Z80 microprocessor, which Zilog announced in July 1976.

Even before Zilog announced the Z80 microprocessor, but after the company had working parts, Faggin started to think about the company’s next microprocessors. He wanted to scale complexity up and down at the same time. For scaling up, he wanted a 16-bit processor, which would come to be known as the Z8000. In early 1976, Faggin hired Dr. Bernard Peuto, a computer architect developing IBM-compatible mainframe architectures at Amdahl, to serve as the architect on the Z8000 microprocessor. For scaling down, Faggin took the plans for the 2001 microcontroller off the shelf where they’d been for more than a year, dusted it off, and renamed it the Z8. Faggin and a committee of Zilog engineers including Peuto refined the original architecture for the 2001 microcontroller.

At Intel, Faggin had been adamant about machine-code compatibility between the Intel 8008 and 8080 microprocessors because he was concerned about providing an upgrade path for existing customers who wanted to migrate their code to newer microprocessors. He was not so concerned about instruction-set compatibility for microcontrollers like the Z8. He felt that compatibility didn’t matter for microcontrollers because customers typically did not have legacy software to preserve. (At least not back then. Things are quite different today, four and a half decades later.) Faggin envisioned an instruction set for the Z8 that could manipulate the bits in the microcontroller’s I/O ports directly, without those bits needing to make a round trip through the microcontroller’s accumulator or a register.

Although many online sources say that Zilog announced the Z8 microcontroller in 1979, the company published two in-depth articles about the Z8 in the August 31, 1978 issue of Electronics magazine. The Z8 has a Harvard architecture, like many other early microcontrollers, with separate 16-bit program and data memory spaces. It also had a large, 144-byte register file and could treat any register like an accumulator. Its instruction set and register set do not resemble those implemented in the Z80’s more traditional von Neumann processor architecture.

As a company, Zilog had many ups and downs, but it’s still in business and it still sells microcontrollers based on the Z8 architecture, now called the “Z8 Encore!” Z8 microcontrollers can be found in many low-cost peripheral applications such as keyboards, mice, and infrared remote controls. Some versions of the Z8 microcontroller now cost much less than $1 each in large volumes.

I have some personal history with the Z8 microcontroller. In the early 1980s, I designed a Zilog Z8 into an embedded system for Anatel as a consulting project. It was a total-organic-carbon (TOC) water analyzer, and Anatel wanted a minimal hardware design. The Z8 microcontroller offered the best bang for the buck, at the time. It had far more capability than the Mostek MK3870 microcontroller I’d designed into the HP 98037A Analog I/O card in the late 1970s. It was far more powerful than the Intel 8048, with a far better instruction set, a large register file, separate 16-bit address spaces for program and data memory, and sensible I/O structure that was well suited for embedded applications. Things might have been different if the Intel 8048’s successor, the 8051, had been less expensive at that time, but it wasn’t.

Anatel TOC analyzers are still available, now from Hach, which bought Anatel in 2001. I don’t know if today’s TOC analyzers still use the Z8 as a controller. Hach itself was purchased by Danaher in 1999. That’s often the story in business. The big fish eat the little fish, and then even bigger fish swim by and eat the big fish.

Faggin and Ungerman are long gone from Zilog. Both became entrepreneurs. After leaving Zilog in 1980, Faggin started or ran several companies including Cygnet Technologies, Synaptics, which was an early neural network pioneer that ended up inventing the touchpad, and a spinoff of Synaptics called Foveon, which developed an unusual, multi-layer, color image sensor. Ungermann left Zilog in 1979 and co-founded Ungermann-Bass, a local-area network pioneer. Littelfuse now owns Zilog through its acquisition of IXYS in 2018. IXYS bought Zilog in 2009.

Little fish. Big fish. Bigger fish.



Oral History of Federico Faggin, Computer History Museum, 2004-2005

In Memoriam: Dr. Bernard Peuto, Architect of Zilog’s Z8000 and Z8, Steve Leibson, EEJournal.com, February 19, 2019

“Introducing the Z8, part 1: One-chip microcomputer excels in I/O- and memory-intensive uses,” Bernard L. Peuto and Gary J. Prosenko, Electronics Magazine, August 31, 1978, pp 128-133

“Introducing the Z8, part 2: Rich instructions, nine addressing modes make coding easy,” Charles Bass, Judy Estrin, and Bernard L. Peuto, Electronics Magazine, pp 134-137

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