[Ken Shirriff] Picks Apart Mystery Chip From Twitter Photo

It’s no secret that the work of [Ken Shirriff] graces the front pages of Hackaday quite frequently. He’s back again, this time reverse engineering a comparator chip from a photo on Twitter. The mysterious chip was decapped, photographed under a microscope, and subsequently posted on the internet with an open call to figure out what it did.

[Ken] stepped up, and at first glance, it was obvious that most of the chip is unused, and there appeared to be four copies of the same circuit. After identifying resistors and the different transistor types, [Ken] found differential pairs.

Differential pairs form the heart of most op-amps, and by chaining them together, you can get a strong enough signal to treat it as a logic signal. Based on the design and materials, [Ken] estimates the chip is from the 1970s. Given that it appears to be ECL (Emitter-Coupled Logic), it could just be four comparators. But there are still a few things that don’t add up as two comparators have additional inverted outputs. Searching the part number offered few if any clues, so this will remain somewhat a mystery.

We’ve covered [Ken’s] incredible chip sleuthing before here, such as the Sharp EL-8 from 1969.

Inside An Oscillator With [Ken Shirriff]

We are always glad to see [Ken Shirriff] tear into something new and this month he’s looking inside a quartz oscillator module. Offhand, you’d think there’s not much to these. A slab of quartz and some sort of inverter, right? But as [Ken] mentions, “There’s more happening in the module than I expected…”

If you’ve ever wanted to decap devices, big hybrid modules like these are a good way to get started since you don’t need exotic chemicals to get at the insides. [Ken] managed to break the fragile crystal wafer on the way in. Inside was also a small CMOS IC die. Time to get out the microscope.

If you follow [Ken’s] blog, you know he’s no stranger to analyzing IC dice. The oscillator IC is a pretty standard Colpitts oscillator but it also provides a programmable divider and output drive.

The circuit uses some unusually configured capacitors. [Ken] takes the time to point out CMOS logic structures throughout. If you haven’t seen one of [Ken’s] deep dives before, before, it’s a great introduction.

You can learn more about crystal oscillator theory. We used some test equipment to characterize a crystal a few years ago.

What’s Inside An FPGA? Ken Shirriff Has (Again) The Answer

FPGAs are somewhat the IPv6 of integrated circuits — they’ve been around longer than you might think, they let you do awesome things that people are intrigued by initially, but they’ve never really broke out of their niches until rather recently. There’s still a bit of a myth and mystery surrounding them, and as with any technology that has grown vastly in complexity over the years, it’s sometimes best to go back to its very beginning in order to understand it. Well, who’d be better at taking an extra close look at a chip than [Ken Shirriff], so in his latest endeavor, he reverse engineered the very first FPGA known to the world: the Xilinx XC2064.

If you ever wished for a breadboard-friendly FPGA, the XC2064 can scratch that itch, although with its modest 64 configurable logic blocks, there isn’t all that much else it can do — certainly not compared to even the smallest and cheapest of its modern successors. And that’s the beauty of this chip as a reverse engineering target, there’s nothing else than the core essence of an FPGA. After introducing the general concepts of FPGAs, [Ken] (who isn’t known to be too shy to decap a chip in order to look inside) continued in known manner with die pictures in order to map the internal components’ schematics to the actual silicon and to make sense of it all. His ultimate goal: to fully understand and dissect the XC2064’s bitstream.

Of course, reverse engineering FPGA bitstreams isn’t new, and with little doubt, building a toolchain based on its results helped to put Lattice on the map in the maker community (which they didn’t seem to value at first, but still soon enough). We probably won’t see the same happening for Xilinx, but who knows what [Ken]’s up to next, and what others will make of this.

Ken Shirriff Unfolds A Nuclear Missile Guidance Computer With Impressive Memory

Longtime followers of [Ken Shirriff’s] work are accustomed to say asking “Where does he get such wonderful toys?”. This time around he’s laid bare the guidance computer from a Titan missile. To be specific, this is the computer that would have been found in the Titan II, an intercontinental ballistic missile that you may remember as a key part of the plot of the classic film WarGames. Yeah, those siloed nukes.

Amazingly these computers were composed of all digital logic, no centralized controller chip in this baby. That explains the need for the seven circuit boards which host a legion of logic chips, all slotting into a backplane.

But it’s not the logic that’s mind-blowing, it’s the memory. Those dark rectangles on almost every board in the image at the top of the article are impressively-dense patches of magnetic core memory. That fanout is one of two core memory modules that are found in this computer. With twelve plates per module (each hosting two bits) plus a parity bit on an additional plate, words were composed of 25-bits and the computer’s two memory modules could store a total of 16k words.

This is 1970’s tech and it’s incredible to think that when connected to the accelerometers and gyros that made up the IMU this could use dead reckoning to travel to the other side of the globe. As always, [Ken] has done an incredible job of walking through all parts of the hardware during his teardown. He even includes the contextual elements of his analysis by sharing details of this moment in history near the end of his article.

If you want to geek out a little bit more about memory storage of yore, you can get a handle on core, drum, delay lines, and more in Al Williams’ primer.

Ken Shirriff Explains His Techniques For Reverse Engineering Silicon

When it comes to reverse engineering silicon, there’s no better person to ask than Ken Shirriff. He’s the expert at teasing the meaning out of layers of polysilicon and metal. He’s reverse engineered the ubiquitous 555 timer, he’s taken a look at the inside of old-school audio chips, and he’s found butterflies in his op-amp. Where there’s a crazy jumble of microscopic wires and layers of silicon, Ken’s there, ready to do the teardown.

For this year’s talk at the Hackaday Superconference, Ken walked everyone through the techniques for reverse engineering silicon. Surprisingly, this isn’t as hard as it sounds. Yes, you’ll still need to drop acid to get to the guts of an IC (of course, you could always find a 555 stuck in a metal can, but then you can’t say ‘dropping acid’), but even the most complex devices on the planet are still made of a few basic components. You’ve got n-doped silicon, p-doped silicon, and some metal. That’s it, and if you know what you’re looking for — like Ken does — you have all the tools you need to figure out how these integrated circuits are made.

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Ken Shirriff Chats About A Whole World Of Chip Decapping

Reverse engineering silicon is a dark art, and when you’re just starting off it’s best to stick to the lesser incantations, curses, and hexes. Hackaday caught up with Ken Shirriff at last year’s Supercon for a chat about the chip decapping and reverse engineering scene. His suggestion is to start with an old friend: the 555 timer.

Ken is well-known for his work photographing the silicon die at the heart of an Integrated Circuit (IC) and mapping out the structures to create a schematic of the circuit. We’re looking forward to Ken’s talk in just a few weeks at the Hackaday Superconference. Get a taste of it in the interview video below.

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Ken Shirriff Found Butterflies In His Op-Amp

In 1976, Texas Instruments came out with the TL084, a four JFET op-amp IC each with similar circuitry to Fairchild’s very popular single op-amp 741. But even though the 741 has been covered in detailed, when [Ken Shirriff] focused his microscope on a TL084, he found some very interesting things.

JFETs on the TL084 op-amp

To avoid using acid to get at the die, he instead found a ceramic packaged TL084 and pried off the cover. The first things he saw were four stabilizing capacitors, by far the largest structures on the die and visible to the naked eye.

When he peered into his microscope he next saw butterfly shapes which turned out to be pairs of input JFETs. The wide strips are the gates and the narrower strip surrounded by each gate is the source. The drain is the narrow strip surrounding each gate. Why arrange four JFETs like this? It’s possible to have temperature gradients in the IC, one side being hotter than the other. These gradients can affect the JFET’s characteristics, unbalancing the inputs. Look closely at the way the JFETs are connected and you’ll see that the top-left one is connected to the bottom-right one, and similarly for the other two. This diagonal cross-connecting cancels out any negative effects.

[Ken’s] analysis in his article doesn’t stop there though. Not only does he talk more about these JFETs but he goes over the rest of the die too. It’s well worth the read, as is his write-up about the 741 which we’ve also covered.