Going through a collection of old parts, CuriousMarc encountered some ICs that he couldn't identify. He opened up one of these ICs, and I studied it under the microscope. After some reverse engineering, I determined that it was a logic chip that implemented four NAND gates using old-fashioned diode-transistor logic (DTL).1 The chip turned out to be the ST680A, a member of the Signetics 600 series of chips from 1965. In this article, I discuss the circuitry in this chip and how diode-transistor logic works. The die of the ST680A under the microscope. Integrated circuits can be packaged in many ways. One of the most popular is the plastic DIP (Dual In-line Package), a black rectangle of epoxy with two rows of metal pins. This type of package was invented by Signetics: "Introduced in late 1965, the 600 series was the first integrated circuit family to be offered in a solid, plastic, dual in-line package (DIP)." Earlier integrated circuits were packaged in round metal cans or in small flat-packs. In 1965, engineers at Fairchild invented the DIP, which had two rows of pins on 0.1" spacing. Unlike the surface-mounted flat-pack, the DIP had pins that were inserted into holes, making manual or automated assembly quick and easy. Because the pins of a DIP were on a regular grid, rather than the circular pattern of a metal can, circuit board design and manufacturing were also easier (details). The first DIP chips had ceramic packages. The plastic DIP, introduced by Signetics, was much cheaper and became very popular. An advertisement for the Signetics 600 series. From Electronics, March 21, 1966. The plastic DIP is less popular with me, however, because it is harder to open. With a ceramic package, I can simply tap it with a chisel and pop it open, but that doesn't work with epoxy packages. An epoxy package can be dissolved with nitric or sulfuric acid, but I try to avoid dangerous acids. Instead, CuriousMarc used Antoine's hot air decapping method. Unfortunately, the hot air technique doesn't always work. In this case, tiny bits of epoxy were stuck to the die, obscuring the circuitry. I used a few drops of boiling sulfuric acid to clean the die. (I'm okay with sulfuric acid in tiny quantities.) The die on its metal frame. The photo above shows the silicon die on its metal frame, the lead frame. The golden blobs are where the bond wires were attached to the die. You can see the doped silicon regions that form diodes and bipolar NPN transistors, as well as 16 resistors in the center, forming serpentine paths. Most chips have a passivation layer—a thin layer of silicon dioxide—over the chip. Inconveniently, this old chip didn't have a passivation layer, so the acid also stripped off the metal layer. (A few remnants are visible in the upper left.) Without the metal layer, I had to guess at how the components were connected to form logic gates. The die has very faint color differences where the silicon was protected by the metal, so that helped. Eventually, I came up with the diagram below, showing how the metal layer was probably configured. This wiring reveals that the chip implements four DTL NAND gates, which I'll describe in more detail below. One puzzle was that the chip has two unused diodes, indicated with question marks below. The metal layer for a quad NAND chip. I desaturated the image to make the labels clearer. Transistors, diodes, and resistors In this section, I'll explain how the patterns in the image correspond to components of the circuit. The silicon die is doped with various impurities to form regions with different electrical characteristics. These regions appear red or green under the microscope due to thin-film effects. As a result, the chip's transistors, diodes, and resistors are visible. The chip is made from bipolar NPN transistors, which have a completely different construction from the MOS transistors in modern ICs. In an NPN transistor, the current from the collector to the emitter is controlled by the current through the base. The collector is a large region of N-type silicon, silicon that is doped with atoms such as phosphorus or arsenic. Since these elements have one more valence electron than silicon, they give the silicon more negative charge carriers, so it is called N for negative. The N-type silicon happens to appear reddish. On top of the collector, the base is a thin region of P-type silicon, which appears green. This silicon has been doped with atoms such as boron or gallium, which have one fewer valence electron than silicon. The missing electrons form "holes", which act as positive charge carriers. Finally, the emitter is N-type silicon, on top of the base layer. These layers work together through semiconductor magic, amplifying the base current. Two NPN transistors on the chip. The second transistor is a larger output transistor. The chip's output transistors are slightly larger so they can sink more current. In the transistor on the right above, note that the collector contact wraps around three sides of the transistor. The emitter is also larger, with an L-shaped contact. According to the datasheet, each output transistor can sink 2.5 mA of current. The chip uses many diodes since it is diode-transistor logic. The structure of a diode is similar to a transistor, but without the emitter. In a diode, current flows from the cathode (P-type silicon) to the anode (N-type). A diode and a resistor on the chip. The chip uses 16 resistors, located in the middle of the die. A resistor is constructed from a long, thin region of doped silicon. Since silicon has moderately high resistance, a long strip of silicon acts as a resistor. Most of the resistors have a serpentine layout to fit a long resistor into a smaller area. These resistors consist of P-type silicon (green) in a "tub" of N-type silicon (red). The tub is connected to the positive voltage supply; since current doesn't flow from N-type silicon to P-type silicon, this isolates the resistors from each other. Operation of a DTL gate Logic gates can be created in many ways. The earliest integrated circuits (such as the ones in the Apollo Guidance Computer) used Resistor-Transistor Logic (RTL), where logic gates were constructed from resistors and transistors. In March 1962, Signetics announced the first family of commercial Diode-Transistor Logic (DTL) integrated circuits (details). By using diodes on the inputs instead of resistors, DTL provided better performance than RTL. However, DTL soon became overshadowed by TTL (Transistor-Transistor Logic), which was faster and used less power. (If you built digital circuits a few decades ago, you're probably familiar with the popular 7400 series of TTL chips.) The diagram below shows how the DTL NAND gate works. If both inputs are high, the current from the first resistor flows through the base of the first transistor, turning it on. The transistor amplifies this current, passing a much larger current from the transistor's collector to the transistor's emitter. This current goes through the base of the second transistor, which turns on the second transistor. The second transistor passes an even larger current from the output pin to ground, pulling the output pin low. The DTL NAND gate with both inputs high. The schematic is from the datasheet. This circuit is considerably more complicated than the DTL gate on Wikipedia. But if one of the input pins is pulled low, the current from the resistor goes through the diode instead of the transistor. The first transistor turns off, and without a base current, the second transistor turns off. The third resistor pulls the output high. Thus, the output is low only if both inputs are high: a NAND gate. The DTL NAND gate with an input low. I'll point out a few features of this circuit. The diodes on the inputs ensure that one input doesn't affect the other input. The diode in the middle raises the voltage on the first transistor's emitter, so it requires more voltage to turn on, reducing the sensitivity to noise. The output uses a resistor to pull the output high; more advanced circuits use another transistor. When the output is low, the third resistor is still "trying" to pull the output high, which is wasting power. Moreover, the resistor limits the output current, so the high output is fairly weak. In some DTL families, you can get gates with different values for the output resistor, so you can select the tradeoff between wasting power and having an output that is too weak. If you've used TTL integrated circuits from the 1970s, you know that chips usually have power and ground on diagonal pins: ground on pin 7 and power on pin 14. (Putting power and ground diagonally opposite both helps die layout and circuit board layout.) Much to my surprise, I found that the Signetics chips predate this standard and have ground on pin 1 and power on pin 8: still diagonal, but the wrong diagonal! The diagram below shows how the four NAND gates are wired in the chip. Pinout of the 680A quad NAND gate. From the databook. Three chips from one die When I examined the die under the microscope, I figured out the circuit, but I was puzzled by two extra diodes, as if two NAND gates had a third input that wasn't used. The explanation is that Signetics used the same silicon layout for at least three different chips, applying a different metal layer for different functionality. This saved money since it's much cheaper to produce a single optical mask for the metal layer than a complete set of new masks. Signetics sold semi-custom ICs to customers, using an approach called variFEBS (Variable Functional Electronics Blocks). This approach used a custom metal layer on top of fixed silicon, providing custom circuits without the cost of a full mask set. These circuits didn't sell well, but Signetics used the same approach for standard ICs. Pinout of the 670A triple NAND gate and the 616A quad NAND gate. All three chips have some similarities, such as using pins 2 and 14 as outputs. From the databook. One IC with the same silicon as the quad NAND gate is the 670A chip, which has three NAND gates, each with three inputs (above left). The diagram below shows how the silicon can be wired to provide this functionality. The hypothesized metal layer for the 670A triple-NAND gate. The layout for the triple chip above is a bit tricky because the top gate has inputs on both sides of the power (Vcc) pin. This creates a layout problem because the power and ground metal runs vertically to the resistors, blocking metal wiring from one side to the other. The solution is a "crossunder", a region of silicon that allows a signal to pass under the metal layer, connecting the inputs on the left to the rest of the circuitry on the right. This crossunder is visible near the top of the chip. Another chip with the same layout is the 616A dual NAND gate, with five inputs on each gate. Since this chip has 10 inputs in total (compared to 8 on the quad gate), this chip uses the two "extra" diodes that I spotted. If that isn't enough inputs, each NAND gate has an expansion input; by connecting external diodes to the expansion input, the gate can be made as large as desired. The hypothesized metal layer for the 616A dual-NAND chip. Some history The history of Signetics is closely tied to Fairchild. The story of Fairchild's founding is well known: in 1957, eight engineers—the Traitorous Eight—left Shockley Semiconductor and created Fairchild Semiconductor. Hundreds of companies (the "Fairchildren") were started by engineers who left Fairchild. Signetics was one of those companies, formed in 1961 and said to be the first company to exclusively design and manufacture integrated circuits.2 Signetics announced its first product in 1962, a NAND gate that cost $125 (over $1000 in current dollars).3 Not surprisingly, sales were weak. Signetics soon ran short of money, so in 1962, Corning Glass invested $1.7 million for 51% ownership of Signetics. Corning Glass may seem like a strange investor, but Corning was more of a high-tech company than you'd expect, making components such as resistors and glass capacitors, and later creating fiber optics. Moreover, in the early 1960s, integrated circuits were the hot area (much like AI now), and everyone wanted to get involved. In 1963, the Department of Defense pushed for contractors to use integrated circuits in new products. Riding this wave, Signetics became the leading producer of integrated circuits.4 However, Fairchild soon introduced a series of DTL chips that competed with Signetics. The Fairchild 930 series was faster than the Signetics chips and less than half the price, so Fairchild took much of the market from Signetics and dominated the IC market. Signetics also produced analog integrated circuits. Signetics is probably best known for creating the 555 timer chip in 1970, said to be the world's most popular IC, with billions sold.5 Signetics was acquired by Philips in 1975, and then Philips Semiconductors was spun off as NXP (Next exPerience) in 2006. NXP is currently the #10 semiconductor manufacturer worldwide, so the heritage of Signetics lives on. For more, follow me on Bluesky (@righto.com), Mastodon (@[email protected]), or RSS. Thanks to CuriousMarc for providing the IC and thanks to TubeTime for finding the databook. AI statement: Despite the presence of the em dash, no AI was used in the writing of this article (details). Notes and references After I had reverse-engineered the chip, TubeTime found datasheets for it, making my reverse engineering unnecessary. (See the Signetics Condensed Catalog 1969, Utilogic II Databook 1971, and Utilogic 2 Databook 1972.) We must have been unlucky with our original web searches since we didn't find anything. But this way you get to see what's inside the chip :-) The Signetics ST680A IC in its package. The large circular depression marks pin 1. From the date code, this chip is from 1971.  ↩ For more Signetics history, see Signetics Founding History, written by Lionel Kattner, a co-founder of Signetics. He states that the company name was inspired by the words "signals" and "networks", as well as the high-tech suffix "-netics". ↩ See History of Semiconductor Engineering, page 156. ↩ The book Making Silicon Valley describes the history of Signetics. It has a negative view of the Corning investment, saying that Signetics executives "Van Poppelen and Kattner dissented on the grounds that Corning was not a good fit for an integrated circuit company. In their view, Corning was a staid Eastern firm, ignorant about semiconductors and antithetic to the ways and culture of the electronics industry on the West Coast. Their view later proved to be correct." ↩ The 555 timer was created by analog IC wizard Hans Camenzind. If you're interested in analog circuits, you should read his book Designing Analog Chips, which you can download for free. ↩

Why the world peace depends on small counties’ not taking sides?

Ultimately, the Democrats are no more capable of addressing the root causes of popular anger than the Republicans. State power will continue to swing back and forth more and more wildly between different parties until our rulers consolidate an autocracy or we manage to effect revolutionary change. As we anticipated in April, the death knell of the Trump era has rung. Despite being historically unpopular, Democratic politicians won a sweeping victory in the November 2026 midterm elections. Many are describing the rout as an “extinction-level event” for the Republican Party. All this should feel familiar. Only two years ago, when Democrats lost the 2024 elections, pundits across the political spectrum rushed to declare the collapse of the Democratic Party. Summarizing a widespread perception, one expert claimed that “Fundamental shifts are occurring in the body politic that have left Democrats on the wrong side of the popular vote, congressional races, and the country’s shifting demographics.” Two years later, people are saying the same things about the Republican Party. The backlash against Republicans in this year’s election eclipses the gains they made in 2024. Yet the pendulum has been swinging wildly back and forth between parties for over a decade now—and it could be that the wildest swings have yet to come. For all the talk of political polarization, loyalty to political parties is at its lowest in decades. Since at least 2016, anger at the status quo has been the most powerful force in politics; Democrats like Hillary Clinton and Joe Biden who attempted to present themselves as its defenders have learned that the hard way. Likewise, Donald Trump has only able to win elections when he is not in office. Whenever Trump represents the ruling order, he draws the same backlash that he once managed to channel. Since 2014, we have argued that state power itself has become a hot potato that burns whoever holds it. In a globalized economy, in which governments can no longer mitigate the impact of capitalism on their citizens without investors taking their money elsewhere, no party is able to hold state power for long without losing credibility with voters. Similarly, the challenges of maintaining position as a waning imperial power inevitably undercut the legitimacy of whoever controls the state: just as the genocide in Gaza damaged the Biden administration’s support, Trump’s war with Iran has contributed to driving away voters. Similar things are taking place all around the world. British politicians have also seen rapid reversals in fortune. The centrist parties that have long ruled Germany and France are in precipitous decline. One Latin American government after another has swung to the far right, but that hardly indicates a social consensus in favor of any political camp. Only countries under continuous autocratic rule, such as Russia, Belarus, China, and North Korea, are excepted from the hot potato pattern. Donald Trump has made no secret of his desire to establish a similar state of affairs in the United States. Yet even in Hungary, which Republicans took as a model for their illiberal aspirations, the long-running autocratic government ultimately lost control. The same has occurred in Poland and, more recently, Serbia. Wherever voters have an opportunity—however narrow—to demand change, they do so—however arbitrarily and capriciously. With no prospect of improving life for his rank-and-file supporters, Trump’s solution was to inflict violence on their behalf, offering them the vicarious thrill of watching the state cause harm to others as an outlet for their frustration. Less bread, more circuses. Republicans and Democrats—trash and recycling. It might have worked—if ordinary people had not courageously taken the streets to interfere. We owe Trump’s failure to those who assembled at Tesla dealerships in spring 2025, who rose up against federal agents and the National Guard that June, who confronted Immigration and Customs Enforcement mercenaries in Chicago, Minnesota, and elsewhere. As we previously saw in the movement against police and white supremacy, when people take risks in solidarity with others, this makes it possible for more people to experience empathy where previously, they only felt dissociation and apathy. The grassroots resistance that emerged in response to the Trump administration stands in stark contrast to the way that elite figures across the political spectrum immediately put themselves as Trump’s disposal. Tech billionaires from Silicon Valley flocked to his inauguration to throw themselves at his feet. Powerful law firms, university administrations, and corporations subordinated themselves to his will. Heads of state from across the world groveled and toadied to Trump—regardless of how he treated them, no matter how absurd his demands. Throughout 2025, Democratic politicians confined themselves to expressing opposition in purely symbolic ways, if occasionally at great length. Cowardly centrist Democrats had already embraced Trump’s anti-immigrant politics well before the 2024 election; after it, many of them actively participated in the Trump regime’s attacks on immigrants, seizing the opportunity to call for the Democratic Party to continue tacking rightward. The scale of subsequent resistance to ICE showed that this was not hard-nosed pragmatism, but political opportunism at the service of xenophobia. A poll at the beginning of March 2026 showed that only 39% of respondents opposed abolishing ICE, with fully 50% actively calling for its abolition. The disparity between these figures and the very small number of politicians prepared to consider abolishing ICE even today shows that Democratic politicians will openly defy their supporters’ wishes in order to continue to advance a reactionary agenda. As politicians, they do not simply answer to a constituency of voters, but above all to a clientele of capitalists. Trump did his best to rig the system in his favor ahead of the 2026 elections, arranging for widespread gerrymandering, seeking to control the voting process, and attempting to put the pieces in place to contest the results. Billionaires backed him financially—Elon Musk singlehandedly spent half a billion dollars, a quarter of the entire Republican budget for the election, in an effort to put his thumb on the scales. In the end, the results were so conclusive that none of this mattered. As in 2016, 2020, and 2024, the majority of voters rejected the reigning party. Yet because this will was expressed via voting, rather than through more direct means, the result simply hands power to another coterie of politicians who will not address the needs of those who elected them. The more secure the Democrats’ grip on power becomes, the less they will concern themselves with the wishes of the electorate. If anything, the 2026 election will only embolden the centrists within the party, as it put power in the hands of more moderate Democrats, especially in swing districts. But those who imagine that the Democrats did so well in the 2026 election on their own merits are fooling themselves. The core issue at the root of the hot potato pattern is that the existing political order cannot address the instability, disparities, and crises of a capitalist system that has concentrated most of the wealth of society in the hands of a few while inflicting grievous social, psychological, and ecological damage on the rest of us. No political party will initiate the kind of revolutionary transformation that will be required to shift to a more egalitarian and sustainable way of life; such change can only come from grassroots mobilization. As long as there is no widespread, powerful social movement that offers the prospect of addressing these problems through profound change, people will continue rejecting one government after another in increasing desperation. Silicon Valley tech moguls—who backed Joe Biden in 2020 only to switch sides in 2024—are even less popular than Donald Trump. Hatred of tech billionaires, data centers, and Flock cameras cuts across political lines; like the war on Iran, it is one of the factors that caused many former Trump voters to stay home or vote for Democrats. Yet as they regain their hold on power, Democrats will be inclined to work more and more closely with capitalists and the tech industry, rhetoric about “oligarchy” notwithstanding. If social movements die down again as they did in 2021 after Biden took office, this will bode ill for the future, opening the way for even more extreme far-right reactionaries to pretend that they represent the only alternative to an unendurable status quo. If the cycle that played out between the first and second Trump administrations repeats itself again, the third iteration of far-right reaction will be more horrific than we can possibly imagine. For good or ill, it does not look like anyone will be able to delude themselves into believing in a “return to normal” any time soon. The accession of Stephen Miller, an avowed white supremacist, to White House Chief of Staff sets the stage for the Trump administration to conclude with a period of brutal, open conflict. The administration lacks the support to win an open power struggle with the rest of society, but has left itself no alternative. As one New York Times commentator put it, “The next two years could actually be pretty volatile.” As long as Trump remains in power, the far right will be perceived as the hegemonic force against which social anger will gravitate. But we must not wait for Democratic politicians to stand up to the Trump administration; even if they did, at best, that would function to relegitimize the same state institutions that will once again be turned against us in the future—as we saw in the Democrats’s response to the failed coup of January 6, 2021. We must set an example by continuing to resist the Trump administration—and, wherever necessary, Democratic local and state administrations as well—through grassroots direct action. Rather than simply waging a defensive struggle, we must figure out how to take proactive steps towards a completely different way of life in the process. Otherwise, the far right will eventually benefit once again from the inevitable disillusionment with Democratic administrations. In short: it’s good to see Trump losing control. But the pendulum will continue to swing back and forth between political parties in wilder and wilder oscillations until we make revolutionary changes in our society.

Hey folks! Fireside this week, as we’ve (finally) brought the Hearts of Iron IV (I, II IIIa, IIIb, IVa, IVb) series to a close. We may have rather more firesides and even some gap weeks in the next month or two, both due to the end of the semester but also due to some personal … Continue reading Fireside Friday, November 6, 2026 →

It’s hard to deny that something really bad occurred in the Chinese military: the sheer scope of what the Chinese press calls 落马 (luòmǎ, literally “falling off the horse”) is hard to believe.