A past story of MCU

Source: The content is compiled by Semiconductor Industry Review (ID: icbank) from eejournal, thank you.

Gary Boone, who worked in the MOS division of Texas Instruments (TI), designed the first chip that could be called a microcontroller because he was tired of his work and his family was in trouble. He joined TI in 1969 when calculator chips were becoming a big business. In the 1960s, electronic calculators replaced the Marchant and Friden mechanical calculators that had dominated the market for decades. Semiconductors enabled the replacement of hundreds of complex metal and plastic parts in mechanical calculators, first with hundreds of transistors and diodes, and then with fewer and fewer integrated circuits. North American Rockwell Microelectronics, Mostek, General Instruments, and Texas Instruments were early participants in the multi-chip calculator market.

At first, it took dozens of integrated circuits to replace hundreds of transistors and diodes. As more and more components were included in integrated circuits, the number of integrated circuits needed to make a usable calculator also decreased. By 1968, IC-based calculator designs largely replaced transistor-based designs. The end goal was clear. Eventually, semiconductor manufacturers would simplify the electronic core of calculators into a single chip.

Japanese calculator suppliers Sharp, Canon, and Busicom cooperated with various American semiconductor suppliers to develop custom chips for their calculators. Sharp cooperated with Rockwell, Canon with TI, and Busicom with Mostek and Intel to develop different models of calculators. Busicom asked Mostek to develop a single-chip calculator and signed a contract with Intel to develop a custom chip set for a more complex programmable calculator. At the end of 1970, Mostek achieved this goal for the first time, launching the MK6010, a custom chip that replaced 22 integrated circuits. Busicom integrated this chip into its small four-function desktop calculator, Busicom Junior. The contract with Intel eventually led to the development of the Intel 4004 microprocessor. However, this story is about microcontrollers, which took a related but different evolutionary path.

TI's MOS division was deeply involved in calculator chip sets. Calculator companies including Canon, Olivetti, and Olympia asked TI to develop 4, 5, and 6 chip sets for their calculators. The task of executing these custom chip projects fell on the shoulders of several TI engineers, including Gary Boone. This job required flying around the world to Japan, Italy, and Germany. Boone spent a lot of time on the road, and his family was unhappy with his absence. Boone quickly became tired of the intense travel, just to develop a new chip set that looked similar to the previous one. In those days, many potential customers wanted calculator chips, but each customer wanted something a little different. This is the nature of the custom chip business. It is a customer-intensive industry.

Boone's frustration and family affairs prompted him to find TI's MOS market manager Daniel Baudouin. Together, they compiled a customer demand matrix, which came from the needs of different calculator manufacturers. Then, they added a set of functional blocks that could meet these needs. Boone and Baudouin also noticed what the current TI MOS process technology could do and what it could do best. Their thinking quickly turned to architectures that use a lot of memory (RAM and ROM), because these structures are highly efficient, easier to wire on ICs, and memory is expected to increase the utilization rate of silicon to 40 or 50 times.

Once Boone and Baudouin started considering the use of memory, they began to consider how much data and program storage space a calculator chip needed. At that time, the TI team began to discuss with potential customers the prospects of a single-chip calculator with ROM programmability. They encountered a lot of opposition. Customers who were accustomed to funding their own calculator chips were hesitant about the idea of calculator chips that were only distinguished by some bits in the on-chip ROM. There was also opposition within TI, because ROM-based programmable parts were the opposite of what the company was used to manufacturing.

Reading this, you may find that all the discussions about calculator chips are inconsistent with the title. This series of articles is obviously about the history of microcontrollers. I assure you, we have not deviated from the track. The earliest microcontrollers were designed by Boone and TI engineer Michael Cochran, including the processor, memory (RAM and ROM), and I/O all on a piece of silicon, which were calculator chips, they were the earliest microcontrollers. See the figure below, excerpted from US Patent 4074,351:

Image source: United States Patent and Trademark OfficeThis diagram shows the block diagram of Texas Instruments' (TI) first microcontroller calculator, the TMS1802NC. It displays all the key components of the microcontroller. It has a Central Processing Unit (CPU), which consists of a Program Counter (PC), Instruction Register (IR), Instruction Decoders, and a 4-bit Arithmetic Logic Unit (ALU). It has Random Access Memory (RAM) for storing numerical data and Read-Only Memory (ROM) for storing programs that define the operation of the chip. Finally, at the bottom, you can see dedicated I/O circuits for scanning a matrix keyboard, driving display digits, and driving the seven segments in each display digit. The I/O in this design may be specialized, but the diagram clearly describes a microcontroller.

On September 17, 1971, TI released the TMS1802NC microcontroller calculator integrated circuit. Two months later, Intel released the 4004 microprocessor. Texas Instruments priced this device at less than $20. The ROM contains 320 11-bit instruction words (3520 bits), and the serially accessed 182-bit RAM contains 3 13-digit BCD (Binary-Coded Decimal) numbers and 13 binary flag bits. The chip required approximately 5,000 transistors in total.

(Note: While researching this article, I found that more than one website has confused TI's TMS1802NC 4-bit calculator chip with the 8-bit RCA CDP1802 COSMAC CMOS microprocessor released in 1974. The TI and RCA chips are not the same part, despite the similar part numbers.)

Further confirmation of the TMS1802NC as a microcontroller comes from TI's press release on September 17, 1971:

"TI uses the same base or host design of single-level mask programming technology, which can easily implement any number of special operational features. The only limitation is the size of the program ROM, RAM storage, control, timing, and output decoders. For example, by reprogramming the output decoder, the TMS1802 can be used to drive decimal displays, such as Nixie tubes."

One of the earliest calculators to use the TI TMS1802 calculator chip was the Sinclair Executive.

The Sinclair Executive was a very early pocket calculator that included the TMS1802 microcontroller calculator. Image source: MaltaGC, Wikimedia Commons

TI released the TMS0100 microcontroller calculator series on September 20, 1972, almost exactly one year after the release of the TMS1802C. The company renamed the TMS1802NC as the first member of the TMS0100 family, the TMS0102. Eventually, this family would have more than 15 different members, made using TI's 10-micron PMOS process technology. A year later, Mostek released an improved, pin-compatible copy of the TMS0102, the MK5020. Like all the semiconductor manufacturers listed at the beginning of this article, TI and Mostek would soon release microcontrollers, partly developed using knowledge gained from the creation of these early calculator chips.

In the meantime, Boone had already stepped out of the calculator box. Calculator chip patent 4,074,351 described other target applications, including taxi meters, digital voltmeters, event counters, car odometers, and measuring scales. Of course, microcontrollers have been used in all these applications and far beyond.

Like many pioneering devices, Texas Instruments' TMS0100 calculator chip family was a narrow microcontroller, mainly used for making calculators. However, the first chip of the TMS0100 family, initially called TM1802NC and later renamed TMS0102, contained everything needed for a microcontroller: CPU, RAM, ROM, and I/O. Of course, this was a specialized microcontroller. Its I/O was application-specific, designed to connect to a matrix keyboard and a seven-segment display. However, the TMS1802NC was a microcontroller.Originally conceived by Gary Boone and Daniel Baudouin of Texas Instruments, and then realized by Boone and Michael Cochran, Texas Instruments launched the TMS0100 series on September 20, 1972. These chips quickly dominated the calculator market. TI suddenly had an entirely new world to conquer. The company soon realized that if the same programmable silicon could be designed to be versatile enough, it could serve multiple markets. TI applied the experience it gained from the initial programmable calculator chips to produce the first general-purpose microcontroller series, the TMS1000, which was released in 1974.

The TMS1000 microcontroller series has some similarities with the TMS0100 programmable calculator series, but there are also many differences. Both devices have a 4-bit CPU and a Harvard architecture, which provides separate address spaces for RAM and ROM. The Harvard architecture was common in early microcontroller designs because it simplified the design of microcontroller RAM, ROM, address decoders, and data buses. However, in my view, the Harvard architecture complicates the lives of programmers who must track two different address spaces and often design methods to transfer data from ROM to RAM. (Fortunately, transferring data from RAM to ROM is meaningless, and data will not complete this process. You cannot successfully write to a masked ROM.)

Unlike the 3250-bit ROM of the TMS0102 (organized as 320 11-bit words), the first TMS1000 microcontroller had a 1-kilobyte ROM, organized as 1024 8-bit words. Therefore, the TMS0100 and TMS1000 series started with incompatible 11-bit and 8-bit instruction sets, respectively. Similarly, the 182-bit serial RAM of the TMS0102 contains three 13-digit numbers in BCD (binary-coded decimal) format and 13 binary flags, while the TMS1000 microcontroller has 256 bits of RAM organized as 64 4-bit words.

According to the TMS1000 documentation, the 64 4-bit words stored in RAM are "conveniently grouped into 4 files of 16 bits each, addressed by a 2-bit register." Based on my experience, when writing similar microcontroller architectures (which will be discussed later in this series), further dividing the small RAM address space into blocks of 16 words is not particularly convenient unless you are writing a circular buffer for 16 entries. Like many design compromises, the microcontroller design team crammed the entire CPU, along with RAM, ROM, and I/O circuits, onto early semiconductor molds, and I would bet that this particular design choice made the hardware design of the TMS1000 microcontroller simpler and smaller, usually at the expense of programmer convenience for the sake of hardware design convenience.

Unlike the dedicated I/O design of the TMS0100 calculator chip series, the TMS1000 microcontroller has general-purpose I/O pins, at least in name. Four input pins (K1, K2, K4, and K8) can be read as a group with a single instruction. The output pins are more complex. The initial TMS1000 microcontroller has 11 "R" outputs (R0 to R10) and 8 "O" outputs (O0 to O7). "R" outputs are set and cleared individually. "O" outputs are controlled by a mask-programmed PLA and driven by a 5-bit latch. Four bits of the latch can be set with a single instruction that moves data directly from the TMS1000's accumulator to the latch. The fifth output bit comes from the ALU's status latch. Using a PLA to expand the 5-bit output latch to 8 output pins is reminiscent of the TMS1000's heritage as a calculator chip, designed to drive 7-segment displays.

Among Adam Osborne's many accomplishments, he documented early microprocessors and microcontrollers in his 1978 book, "An Introduction to Microcomputers." In his description of the TMS1000, Osborne seems more focused on the microcontroller's limitations:

"The fact that the TMS1000 series microcomputers are single-chip devices has some minor, not-so-obvious implications. Most importantly, there is no such thing as support equipment. 1024 or 2048 bytes of ROM [the TMS1200 microcontroller has 2Kbytes of ROM] represent the exact amount of program memory that will appear; no more and no less. Similarly, 64 or 128 bytes of RAM (a byte is a 4-bit word) cannot be expanded. Direct memory access logic does not exist—and its existence would make little sense anyway; with the small total amount of available RAM and ROM, there is simply no opportunity to transfer blocks of data for a long enough time to justify bypassing the CPU.

Similarly, in the TMS1000 microcomputer, the role of interrupts is trivial. Given the small amount of available program memory and the low cost of program packages, it is difficult to justify the complexity of interrupt logic just so that the microcomputer can perform multiple tasks."

In my view, Osborne's words suggest that many people (possibly including Osborne) did not clearly understand the difference between microcontrollers and microprocessors in 1978 when he published that book, four years after TI first announced the TMS1000 series. However, many people did understand the difference, as it is reported that by 1979, TI was producing tens of millions of TMS1000 units per year, selling them in large quantities at prices of $2 or $3 each. The low unit cost of the TMS1000 was possible, partly because TI packaged the device in a cheap 28-pin plastic DIP.Texas Instruments (TI) offered a low-cost TMS1000 microcontroller in a cheap 28-pin plastic DIP package. Image source: Antonio Martí Campoy, Wikimedia Commons.

TI practiced what it preached by using members of the TMS1000 microcontroller family in some of its own consumer products, including the legendary TI Speak & Spell game and the SR-16 "electronic slide rule" calculator.

TI created the TI Speak & Spell using its own TMS1000 microcontroller. Image source: FozzTexx, Wikimedia Commons.

Inventor, game designer, and "father of home video game consoles," Ralph H. Baer realized that he could make affordable electronic games with microcontrollers and integrated the TMS1000 into one of the most successful handheld electronic games— Milton Bradley's Simon, which was launched in 1978. Nowadays, everyone plays handheld games on their smartphones, but back then, these games required dedicated hardware.

Milton Bradley's handheld electronic game, Simon, was an early product that utilized TI's TMS1000 microcontroller. Image source: shritword, Wikimedia Commons.

Parker Brothers released the handheld electronic game Merlin in 1978, based on the TMS1000 microcontroller. A year later, Milton Bradley used the TMS1000 microcontroller as the programmable brain for its Big Trak, a futuristic 6-wheeled tank-like vehicle that could be pre-programmed via a thin-film keyboard embedded on the back of the toy to follow specific paths. Big Trak could execute a sequence of 16 commands inputted on the keyboard, which seems closely related to the turtle graphics of the Logo programming language developed in 1967 by Wally Feurzeig, Seymour Papert, and Cynthia Solomon at a research company named Bolt, Beranek and Newman (BBN) in Cambridge, Massachusetts.

Milton Bradley used the TMS1000 microcontroller in the Big Trak toy vehicle. Image source: Martin Ling, Wikimedia Commons.In 1977, Mattel Corporation launched an extremely successful electronic football game. This game was based on the Rockwell calculator chip, but companies around the world cloned this game. A game manufacturer in Hong Kong named Conic seems to have used the TMS1000 microcontroller in its cloned product instead of the calculator chip. The open-source game simulator MAME (Multiple Arcade Machine Emulator) can still run the TMS1000 ROM code of "Conic's Football" in simulation.

Author Stan Augarten pointed out in his book "State of the Art" that the TMS1000 was used in calculators, toys, games, appliances, anti-theft alarms, copiers, and jukeboxes. Ogata wrote at the end of the description of the TMS1000: "Like any integrated circuit, the TMS1000 helped to make the power of modern electronics available to everyone."

I suspect that there are countless unrecorded applications of the TMS1000 family. For the second early microcontroller family, this is a quite successful story and legacy, which also proves the true universality of the basic single-chip microcontroller concept. After TI launched the TMS1000 in 1974, new microcontrollers launched by other semiconductor manufacturers emerged at a rapid pace.

Now that we have entered the 21st century, most people rarely think about the connection between Rockwell Microelectronics and microprocessors and microcontrollers. The parent company, North American Rockwell (renamed Rockwell International in 1973), was a major military/aerospace contractor. Rockwell built the Apollo spacecraft, B1 bombers, and the U.S. space shuttle.

For a long time, most of the space booster rockets and intercontinental ballistic missiles in the United States used Rockwell's Rocketdyne engines. In 1972, Rockwell launched the world's third commercially successful microprocessor, the 4-bit PPS-4. In 1976, Rockwell released a single-chip microcontroller based on the PPS-4 architecture. It was called the PPS-4/1.

As with the trend of many large corporate groups in the 1960s, Rockwell started its own semiconductor manufacturing business in its independent division in 1967. Autometics developed various military/aerospace avionics systems, including inertial navigation and guidance systems for U.S. submarines and intercontinental ballistic missiles, creating a demand for advanced semiconductors. North American Rockwell Microelectronics Corporation (NRMEC) developed early MOS/LSI process technology for its military and aerospace projects.

When Japan's Sharp approached a semiconductor supplier to manufacture its own designed calculator chip set, NRMEC's MOS/LSI capabilities met Sharp's needs. The result of the cooperation was a four-chip set, which Sharp incorporated into its QT-8D calculator. Sharp released this calculator in August 1968. In fact, some might say that the Rockwell chip set in the Sharp QT-8D calculator opened the era of MOS/LSI. In 1970, Rockwell began publishing a MOS/LSI chip catalog.

As Texas Instruments found on the TMS1000 microcontroller, the leap from electronic calculator architecture to a 4-bit microprocessor, or in the case of Texas Instruments (TI), to a microcontroller, was just a short step. Rockwell announced the 4-bit PPS-4 microprocessor series in August 1972. It was the world's third commercially successful microprocessor, and its launch followed Intel's 4-bit 4004 and 8-bit 8008 microprocessors. Rockwell's "PPS" name means "Parallel Processing System."

There are two points that distinguish Rockwell's PPS-4 microprocessor from its competitors. The first is Rockwell's unique QUIP (Quad Inline Package) device packaging. Rockwell's QUIP chips are easily identifiable by their interlaced leads. Because of their appearance, these chips are commonly referred to as "spiders." In an era where the minimum circuit board wiring and space were about 10 mils, the QUIP lead configuration made it easier to design printed circuit boards for these devices.

The second notable feature is the companion chip developed by Rockwell for the PPS-4 microprocessor. By 1975, the chip set family included the CPU, the clock generator/driving device required for Rockwell's unique four-phase clock, 256x4-bit RAM, 1 and 2 kilobyte ROMs, RAM/ROM combination chips, keyboard and display controllers, printer controllers, general I/O chips, and a 1200 bps analog modem. (The 1200 bps analog modem initiated a long series of modem chips, leading to NRMEC becoming Conexant Systems, which was eventually acquired by Synaptics.)The extensive range of chips in the Rockwell PPS-4 microprocessor family has led to the widespread application of this processor in end products, including cash registers, fax machines, household appliances, pinball machines, toys, and calculators. However, the market for multi-chip, 4-bit microprocessor families was short-lived. Semiconductor technology developed rapidly, and device density increased at an astonishing rate. In October 1975, Rockwell integrated the clock generator into the microprocessor and combined RAM, ROM, and I/O peripherals into a 2-chip set called PPS-4/2. However, due to further advancements in semiconductor process technology, the 2-chip set also had a short lifespan. In early 1976, Rockwell released the PPS-4/1, a true single-chip microcontroller based on the original PPS-4 microprocessor architecture.

The Rockwell PPS-4/1 microcontroller is packaged in the company's unique QUIP (Quad Inline Package), also known as the "spider" chip for obvious reasons. Image source: Christian Bassow, Wikimedia Commons

There is little historical information about Rockwell PPS-4 applications on the internet, except for information about calculators based on the PPS4 and a rather unusual application: Gottlieb pinball machines. Gottlieb contracted with Rockwell to develop the System 1 pinball control board based on the PPS-4/2 microprocessor. Gottlieb used the System 1 board in pinball machines released from 1977 to 1980. The first pinball machine to use the System 1 board was called "Cleopatra." Other microprocessor-based pinball games followed, such as "Sinbad," "Dragon," "Charlie's Angels," "Incredible Hulk," "Buck Rogers," and "Totem." There were a total of 16 pinball games in this series.

Gottlieb's Totem pinball machine used the System 1 CPU board based on the Rockwell PPS-4/2 microprocessor. Image source: Frédéric BISSON, Wikimedia Commons

This is a history that is easily forgotten by time, but the history of PPS-4 as a pinball controller has not been forgotten for two reasons. First, collectors reward Gottlieb pinball machines based on the System 1 board. Second, the metal gates, MOS/LSI PPS-4 rom/ peripheral chips on these boards are failing, and they are now approaching half a century of history. Typically, pinball collectors are stuck with scrapped machines after these parts fail because they have not been produced for decades, and semiconductor supplier NRMEC is long gone.

Gottlieb contracted with Rockwell to design the System 1 pinball control board based on the PPS4/2 microprocessor chip set. Image source: Stephen Emery, ChipScapes.com

A French consulting firm, AA55, has developed a solution to this problem. The company has developed an FPGA-based Rockwell PPS-4 peripheral chip. The FPGA code of AA55 Consulting seems to be targeted by AMD/Xilinx, as the project files are formatted for Xilinx's ISE development software. AA55 Consulting has not yet reverse-engineered the PPS-4/2 processor, but plans to do so in the future. Maybe next year.Due to the fact that Rockwell components are now virtually pure unobtanium, the company NI-Wumpf, located in Honeoye Falls, New York, has developed a functionally equivalent replacement for the original Gottlieb System 1 board, without the use of any Rockwell semiconductors. The original NI-Wumpf board appears to be based on the Zilog Z80 microprocessor. The latest version utilizes the STMicroelectronics STM32F103 microcontroller, which includes a 72 MHz Arm Cortex-M3 processor. For comparison, the PPS-4/2 microprocessor operates at a frequency of 199 kHz. A French company called Flippp! has taken a similar approach, developing board-level replacements for the System 1 board known as the PI-1 and PI-1×4, designed and programmed by Pascal Janin. This board also appears to be based on a more modern microcontroller.

It is interesting to read some comments from users of Gottlieb pinball machines based on the System 1 board. Most people believe that Rockwell was merely a defense contractor in a strict sense. A website called pinwebsite has a forum dedicated to Gottlieb, with a thread titled "Why was Gottlieb's System 1 so bad?" Here are some quotes from this post:

"At the time, Rockwell seemed like a good choice. After all, they designed computer equipment for NASA and the Department of Defense, what could possibly go wrong? Apparently, quite a lot. Rockwell made questionable decisions regarding grounding, using custom-designed components and other strange things, which really messed up Gottlieb."

"Why would Rockwell spend extra time and effort designing custom spider chips when they still weren't as good as the off-the-shelf 68xx chips used by Williams and Bally?" Adopting custom hardware seems hard for them to save costs."

Gottlieb was unaware and made some wrong choices in the outsourcing process. As for Rockwell, you might wonder, what is the greater miracle: the success of the pinball machine or their NASA products?"

I think Rockwell used "off-the-shelf" components for the spider that were "off-the-shelf" for them. Part of the problem may be that they never designed hardware for the environment in which the pinball game is located. Expect switches to fail when they are turned on, rather than slamming shut? Isn't the hardware "off-the-shelf" for anyone outside the defense industry?

"I don't want to be too political, this is just my opinion, if I want to hire a company to design some electronic products for me, even if Rockwell has a good name, I don't want to hire a company that is used to doing government projects. In most cases, they are bloated, expensive, and over-designed. I'm not sure if this was the case in the late 1970s, but just because space equipment works well, it doesn't mean it's not overpriced and over-designed."

"Rockwell designed the system as a 4-bit system - which was outdated before it was released."

Undoubtedly, today's pinball machine collectors do not know that Rockwell was a commercial chip supplier in the 1970s, do not know the long history of the PPS-4, do not know why to develop 4-bit microprocessors and microcontrollers, do not know why Rockwell developed the "spider" QUIP, and do not know that systems that have been poorly maintained for half a century tend to fail. However, some collectors are well-informed. For example:

"In terms of electronics - System 1 uses mid-70s technology. All electronic components are off-the-shelf components, with no custom components. In fact, Rockwell used their own parts - who can blame them? I think it only has two shortcomings - poor grounding technology and edge connectors."As for their CPUs being unpopular—–they were quite popular at the sales points for a considerable period of time. However, when MOS Technology introduced the affordable 6502 series processors, their 4-bit processors were phased out.

Rockwell Microelectronics and the PPS-4 product line have also vanished from the collective memory of people actively involved in the electronics industry, and it is difficult to find the history of PPS-4 online. You almost need to resort to old books. Fortunately, I have some such books on the shelves of my study.

For example, the 1981 edition of the Osborne 4 & 8-bit Microprocessor Handbook lists ten members of the Rockwell PPS-4/1 microcontroller family. Family members have 640 to 2048 bytes of ROM and 48 to 128 4-bit RAM. All members, except one, have three integrated serial I/O ports, which are essentially serial 4-bit shift registers. The MM76C is a family member with a high-speed up/down timer/counter subsystem that can operate as a 16-bit counter or two 8-bit counters. The counter can also handle quadrature encoder inputs used by optical encoders. The timer/counter subsystem has opened up additional industrial application fields for Rockwell PPS-4/1 microcontrollers, including motor control, frequency counting, analog-to-digital conversion, and frequency synthesis.

If you are not familiar with NRMEC, Rockwell Microelectronics, or Rockwell Semiconductor, it may be because the company was spun off into Conexant Systems in 1999, as part of a global effort to bring the value of internally held semiconductor companies to the stock market. Conexant spun off its wafer fab (the former Rockwell wafer fab) into Jazz Semiconductor in 2002, and has since gone fabless. Tower Semiconductor acquired Jazz Semiconductor in 2008 and became TowerJazz. The company resumed the name Tower Semiconductor in 2020, and is now being acquired by Intel. In the meantime, Rockwell's early MOS/LSI processes have become a thing of the past and are mostly forgotten.