Learn Who Will Receive a “Technology Oscar” From IEEE

This article was first published as "Design case history: the Commodore 64." It appeared in the March 1985 issue of IEEE Spectrum. A PDF version is available on IEEE Xplore. The diagrams and photographs of chips, circuit boards, and screens appeared in the original print version.

Charles Winterble, then director of worldwide engineering for Commodore, gave the go-ahead for the chip effort, and Charpentier’s group worked fairly independently until both chips were finished in mid-November 1981.

At a meeting with Charpentier and Winterble late that month, Jack Tramiel, then president of Commodore, decided not to proceed with the video game. Instead, he decided, the chips would go into a 64-kilobyte home computer to be introduced at the Consumer Electronics Show in Las Vegas the second week of January 1982. The computer had yet to be designed, but that was easily remedied.

In two days, the engineers laid out on paper the machine’s basic architecture. Just before the new year, they completed five working prototypes. In the meantime, enough operating-system software was copied and rewritten from the VIC-20 to give passable demonstrations of what the new machine could do. Following its enthusiastic reception at the Consumer Electronics Show, the Commodore 64 was rushed into production; volume shipments began in August 1982 and have continued unabated.

Despite complaints about quality control and the industry’s slowest disk drive, the Commodore 64 has been an unparalleled success, pushing a number of its competitors out of the market. Part of the reason for its success is the price, which keeps falling—from $595 at its introduction to $149 currently, for which the consumer gets graphics and sound equal to or better than that provided by machines that cost five times as much.

Designing the next great chips

In the late 1970s, MOS Technology was a successful semiconductor company; its engineers had designed the popular 6502 microprocessor, and it manufactured several other solidly selling products. Commodore, a West Coast company at the time, took over MOS in 1976—causing many of the MOS engineers to quit when their stock was bought at 10 cents on the dollar—but MOS was allowed to operate fairly autonomously.

In 1979 and 1980, recalls Charpentier, MOS Technology developed the 6510 microprocessor—a minor revision of the 6502 with an additional input-output port, the 6526 peripheral controller, a lot of read-only memory (ROM) chips, and a 4-kilobit random-access memory (RAM) chip. At that time, MOS was supplying equipment to Atari Inc., General Electric Co., Hewlett-Packard Co., and a number of other clients, as well as to Commodore.

When the decision was made to design the latest in superior graphics and sound chips, the first step was obvious: to find what the current high-quality chips could do. In assembling his design team, Charpentier recruited Robert Yannes, a young engineer who had joined MOS in 1979 and had designed the VIC-20 at home, from a spare prototype board. The team spent about two weeks researching comparable chips industrywide.

“We looked heavily into the Mattel Intellivision,” recalls Winterble. “We also examined the Texas Instruments 99/4A and the Atari 800. We tried to get a feel for what these companies could do in the future by extrapolating from their current technology. That made it clear what the graphics capabilities of our machine had to be.”

The MOS designers freely borrowed ideas that they liked—sprites from the TI machine, collision-detection techniques and character-mapped graphics from the Intellivision, and a bit map from their own VIC-20. They then packed as many of those ideas as they could into a predefined area of silicon.

“Al was given the freedom, within a certain die size, to put in everything he could, working backward within the size we planned. When he ran out of registers he stopped,” said Winterble. “We defined in advance the silicon size that would give a yield we were willing to live with; at that time, a die size that was reasonable in 5-micrometer technology was less than 200 mils. Then we prioritized the wish list from what must be in there to what ought to be in there to what we’d like to have, so the decisions that were needed at various points became fairly automatic.”

Nine months to first-pass silicon

For nine months, Charpentier worked with two draftsmen and one computer-aided-design operator on the graphics chip while Yannes worked with two other draftsmen and one CAD operator on the sound chip. They lacked completely the sophisticated design tools of today’s engineering workstations, but they had one readily available design tool found almost nowhere else in the home-computer industry: a chip-fabrication line on the premises. With this, Winterble explained, a circuit buried deep inside the chips could be lifted out and run as a test chip, allowing thorough debugging without concern for other parts of the circuitry. David A. Ziembicki, then a production engineer at Commodore, recalls that typical fabrication times were a few weeks and that in an emergency the captive fabrication facility could turn designs around in as little as four days.

The cost of developing the Commodore 64: No one knows.

The cost of developing the Commodore 64: No one knows. “I had no formal budget accountability,” said Winterble, “other than Jack watching me. Jack said that budgets were a license to steal.” Because MOS Technology’s fabrication facility was not running at full capacity, the equipment used for C-64 test chips and multiple passes of silicon would otherwise have been idle. “We were using people who were there anyway,” said Ziembicki. “You waste a little bit of silicon, but silicon’s pretty cheap. It’s only sand.”

Although custom chips are usually considered expensive, the C-64 chips were not. Not only were development costs absorbed in company overhead, but there was no markup to pay, as there would have been inf the chips had been built by another company. And yields were high because the chips were designed for a mature semiconductor-manufacturing process.

The sound chip was designed with 7-micrometer technology, scaling down to 6 in places. (By contrast, the custom chip for Atari’s Video Computer System, fabricated four years earlier, was built with 6-micrometer technology.) Commodore’s video chip was designed with 5-micrometer features.

Because design time rather than silicon was at a premium, the chips were laid out simply rather than compactly. “We did it in a very modular fashion,” said Yannes. For example, he noted, “the standard way of building oscillators is to build one and then multiplex it until you have as many as you need. We just built an oscillator module and repeated it, because that was much faster than working out all the timing for the multiplexer.”

“What was remarkable,” Winterble added, “was that nine months later, when we came out with the first pass, it functioned except for one bad sprite.”

In November 1981, the chips were complete. The original intent had been a game machine, but at this point the personal-computer market was beginning to look promising. At a meeting of Charpentier, Winterble, and Tramiel, the decision was made to go for a personal computer. The next choice to be made, according to Charpentier, was between a 16-kilobyte and a 64-kilobyte machine, since the custom chips were designed to handle either option.

“Jack made the bet that by the time we were ready to produce a product, 64K Rams would be cheap enough for us to use,” Charpentier said.

When the design of the Commodore 64 began, the overriding goals were simplicity and low cost. The initial production cost of the Commodore 64 was targeted at $130; it turned out to be $135. The computer would use the same case as the VIC-20 and the same-sized circuit board, to speed development. “That wasn’t even a decision,” said Charpentier. “It was just common sense. If you’ve got a product that’s a winner, why change it?” To switch from the VIC-20 to the Commodore 64, the production group had only to make the cartridge slot smaller, change the color of the case, and design a new label.

Furthermore, instead of designing for performance first and price second, as many engineers tend to do, the small design team at Commodore had cost in mind from the beginning. Yannes, for example, had made economy his credo when he was an impecunious high-school student looking for parts to build a sound synthesizer. “Anytime I design something, I want to use the minimum number of components possible. It’s a personal challenge. If there’s a spare gate in a gate package, I’ll work to get rid of the entire package, because in working with a certain number of chips, I ought to be able to use up everything that’s in them. The Commodore 64 was my attempt to build the absolute minimal system that could be built out of the video and sound chips put together.”

Happy New Year 1982!

In the consumer-electronics industry, new products are traditionally introduced to distributors, dealers, the press, and the competition twice a year—during the first weekend in January and the first weekend in June, at the Winter and Summer Consumer Electronics Shows (CESs).

“When you worked for Commodore,” said Yannes, “you always had to have something for the Winter CES.” The C-64 didn’t have much competition at the winter show in 1982. Atari was still sowing its 400/800 computer. Mattel introduced the Aquarius computer, and Spectravideo introduced its computer/game machine, both with limited memory and capabilities.

Ziembicki recalled, “All we saw at our booth were Atari people with their mouths dropping open, saying, ‘How can you do that for $595?’”

“We were a hit,” Winterble added.

After the show, Commodore, which had a reputation for sometimes showing products that never reappeared, had to get the 64 into production quickly. Only a few design changes were made to ready the machine for production. “What’s in the 64 functionally is what I wanted,’ Yannes said. “What’s in the sound chip is what I wanted, and what’s in the video chip is what Al wanted.”

In fact, said Ziembicki, “after it finally got into production, we looked back and asked, why did we bother changing it after January? It wouldn’t have sold one unit less, and we would have saved a lot of money on development costs.”

Some of the changes were fairly significant, but they may have created as many problems as they solved. The biggest improvement was to remedy “a hiccup” in the video chip, said Winterble.

When Charpentier first designed the video chip, he explained, his goal was optimum performance in both black-and-white and color. Previous video chips, such as those used in the Atari and the Apple, had a black-and-white frequency of 7.16 MHz—twice the television color-clock frequency of 3.58 MHz—but this could not squeeze enough characters on a line, and it also induced cross talk between the two signals, causing an object to shift slightly to the left or right on the screen depending on its color. After the January 1982 CES, when he saw that 40 characters wouldn’t quite fit onto a TV screen, Charpentier sped up the black-and-white clock rate and made the two clocks completely asynchronous. But since the color and black-and-white sets of information were constantly changing phase relative to each other, “the color transitions were fantastic, but there was an overall swimming effect,” he recalled. The solution was to put a phase-locked loop into the system so the color and the black-and-white information would have a constant relationship. This, Charpentier acknowledged, was “a Band-Aid solution.”

And that is what it looks like, according to Craig Nelson, director of product development for Epyx Computer Software of Sunnyvale, Calif. “It’s a really elegant circuit,” he said, “except for the phase-locked loop, which is just stuck in the middle of it.” (Commodore now says it has redesigned the chip to eliminate the problem.)

As a result of the “Band-Aid,” the color information and the black-and-white information shift phase by 180 degrees in relation to each other on successive video fields rather than changing phase unpredictably. This conforms more closely to the National Television Systems Committee (NTSC) standard, which requires black-and-white information to have a clock rate that is an odd harmonic of the color-clock rate, so that the two automatically reverse their relationship every other field—one field in phase, the next field out of phase. (In the NTSC standard, colors are determined by the phase difference between the color signal and a color reference signal transmitted at the beginning of each line.)

At the time the standard was developed, commonly available circuitry could not completely separate the black-and-white information from the color: changes in color would lead to changes in brightness and vice versa. It was to average these changes out over time that the NTSC specified that the relative phase reversal of the two signals could occur on successive fields. The result is more pleasing color transitions, but the phase shift makes stationary figures appear to jitter. The jitter is particularly obvious on thin vertical lines, like those in alphanumeric characters. But when the Commodore 64 was conceived, it was to be primarily a game machine, not a computer.

Running a 5-micrometer-technology chip at an 8-MHz clock rate caused it to dissipate a great deal of power—nearly 1.5 watts. Not only did the chip run fast, but to prevent the colors from washing out, as they had in the VIC-20, “we went to 12 volt to drive the heck out of the color signals,” recalled Winterble. “We knew we would have a heat problem.”

At this point Winterble made another design fix—welding a small metal tab onto the inside of the lid of the shielding enclosure around the video chip. When the computer was assembled, the tab pressed against the top of the chip package, forming a heat-conducting path and turning the shielding into a heat sink.

Some changes that might have improved the machine did not get made in the rush to production. For example, Yannes said, the wires for the sound output on the printed-circuit board run alongside the wires for the video signal. As a result, the sound output picks up an annoying 15,750 -Hz whine. Rerouting the circuit would have taken time, “and we had a board that worked,” he explained. “At that point, if you had something that worked, you did not change it.” A circuit-board revision since then has rerouted these lines, Commodore said.

But the designers did in fact change some things that worked—including one revision that degraded the machine’s performance.

But the designers did in fact change some things that worked—including one revision that degraded the machine’s performance. The original design specified a high-quality radio-frequency modulator to transmit the signal to a television set, but a cheaper modulator was substituted. “It was $6.25 to $6.50 for a good one, and we ended up spending about $3,” Charpentier said.

Winterble has a different view of the $3 modulator: “The 50-cent modulator we were using on the VIC-20 wasn’t good enough,” he said, “so we went to a more expensive one.”

Electronic design wasn’t the only difficult area as the Commodore 64 went from prototype development into production—the logistics posed a complex problem. The C-64 was designed in Norristown, Pa., at MOS. The VIC-20 assembly line, which was to begin making C-64s, was in Santa Clara, Calif. As the C-64 went into production, Commodore was also opening a new assembly line in West Chester, Pa. There were additional VIC-20 assembly facilities in Japan, where the disk drive for the C-64 was to be manufactured. And the C-64 circuit boards were being made in Hong Kong.

“It was a lot of fun,” said Ziembicki. “The design people would pick an English screw. The production end would pick metric. But they went with what they had. Commodore production was very good at making things fit whether they were intended to or not. Their charter was 'Ship ‘em’”

“It takes a very tough person,” explained Charpentier, “to say ‘I’m not shipping these because they’re not as good as they could be’—especially when people are clamoring to buy them.”

​Changes continue during production

The start of production of the Commodore 64 in the spring of 1982 did not signal an end to the controversy. “The key is to be able to solve your problems while you are running,” said Ziembicki.

One of the first battles, recalled Charpentier, was over the layout of the printed-circuit board. Commodore’s assembly plant in the United States used automated component-insertion equipment, but its Japanese facility did not, and the two assembly techniques required different component spacing. In the end, the board for the C-64 was laid out for automated insertion, and production was moved to a new plant in Hong Kong that had the automated tools.

Problems also plagued a number of the components—switches, for example. “You pick a switch that’s listed as a consumer switch,” said Ziembicki. “You design it in. You call the manufacturer and get an estimate that sounds reasonable. Then California wants 50,000 a week, but the manufacturer says, ‘We can’t make that. It’s a consumer switch, but we’re not geared for consumer quantities.’ At that point, you’re hung up.”

Since Commodore had just moved its engineering staff from California to Pennsylvania, communication between the design engineers and the production facilities was not very good, Ziembicki explained. "It got to the point where you couldn’t stop working even if you didn’t get an answer---you’d just proceed with the components that you thought the production end could get.”

And outside suppliers were not always reliable. “One provided a power supply for engineering approval,” Ziembicki recalled. “It got approved, and then the supplier changed the design and didn’t tell anybody.”

Charpentier said that his relations with the production group were fairly agreeable. Winterble’s dealings with them were not nearly as cordial, but he found this acceptable. “I personally had to play the heavy on a lot of stuff,” he said. “Then Al would go in and do some good. That technique eased a lot of tension—it was a way to get things done.”

The most notorious problem was “sparkle,” a defect that caused small spots of light to appear on the display screen. The problem was solved before Charpentier left the company in September 1982, but reports of the defect continued well into the Christmas season, with press reports citing it as an example of Commodore’s poor quality control. Canny consumers used it as an excuse to return perfectly good Commodore 64s while they were under 90-day warranty. Since the price of the machine had dropped $200 in the two months following its introduction, this ruse enabled owners to obtain a refund of the purchase price and buy another C-64 at the lower figure.

Sparkle was widely attributed to bugs in the video chip that was the heart of the system, but in fact it was caused by a ROM chip of which 3 million were in service with no problems in other systems, including the hit arcade video game Asteroids. Commodore engineers themselves first looked for the problem in the video chip. It took them three weeks to spot the ROM chip as the source of the defect, Charpentier said. “The problem was a random event—it didn’t happen all the time. We thought the video chip was for some reason seeing the wrong data. We didn’t even suspect it could be the ROM. Finally we put the logic analyzer on it and tracked it down.” The ROM, which Charpentier and his group had designed years earlier, had a special pre-charging circuit to make it run faster, but the circuit made it sensitive to spurious signals.
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