Examining a vintage RAM chip, I find a counterfeit with an entirely different die inside


Ken Shirriff writes, “A die photo of a vintage 64-bit TTL RAM chip came up on Twitter recently, but the more I examined the photo the more puzzled I became. The chip didn’t look at all like a RAM chip or even a TTL chip, and in fact appeared partially analog. By studying the chip’s circuitry closely, I discovered that this RAM chip was counterfeit and had an entirely different die inside. In this article, I explain how I analyzed the die photos and figured out what it really was.”

See the full post on his blog.

A look inside the DS3231 real-time clock


Pete posted an article taking a closer look at Maxim’s DS3231 real-time clock:

Fortunately, Maxim also offers the DS3231, which is advertised as an “Extremely Accurate I2C-Integrated RTC/TCXO/Crystal”. This chip has the 32kHz crystal integrated into the package itself and uses a built-in temperature sensor to periodically measure the temperature of the crystal and, by switching different internal capacitors in and out of the crystal circuit, can precisely adjust its frequency so it remains constant. It’s specified to keep time within 2ppm from 0°C to +40°C, and 3.5ppm from -40°C to +85°C, which means the clock would only drift 63 and 110 seconds per year, respectively. Very cool.

See the full post at HeyPete.com blog.

Inside Intel’s first product: the 3101 RAM chip held just 64 bits


Ken Shirriff writes:

Intel’s first product was not a processor, but a memory chip: the 31011 RAM chip, released in April 1969. This chip held just 64 bits of data (equivalent to 8 letters or 16 digits) and had the steep price tag of $99.50.2 The chip’s capacity was way too small to replace core memory, the dominant storage technology at the time, which stored bits in tiny magnetized ferrite cores. However, the 3101 performed at high speed due to its special Schottky transistors, making it useful in minicomputers where CPU registers required fast storage. The overthrow of core memory would require a different technology—MOS DRAM chips—and the 3101 remained in use in the 1980s.3
This article looks inside the 3101 chip and explains how it works. I received two 3101 chips from Evan Wasserman and used a microscope to take photos of the tiny silicon die inside.4 Around the outside of the die, sixteen black bond wires connect pads on the die to the chip’s external pins. The die itself consists of silicon circuitry connected by a metal layer on top, which appears golden in the photo. The thick metal lines through the middle of the chip power the chip.

See the full post and more details at Ken Shirriff’s blog.

Reverse engineering the 76477 “Space Invaders” sound effect chip from die photos


Ken Shirriff has written an article on reverse engineering the 76477 “Space Invaders” sound effect chip:

Remember the old video game Space Invaders? Some of its sound effects were provided by a chip called the 76477 Complex Sound Generation chip. While the sound effects1 produced by this 1978 chip seem primitive today, it was used in many video games, pinball games. But what’s inside this chip and how does it work internally? By reverse-engineering the chip from die photos, we can find out. (Photos courtesy of Sean Riddle.) In this article, I explain how the analog circuits of this chip works and show how the hundreds of transistors on the silicon die form the circuits of this complex chip.

More details at Ken Shirriff’s blog.

Inside the vintage 74181 ALU chip: how it works and why it’s so strange


Ken Shirriff writes:

The 74181 ALU (arithmetic/logic unit) chip powered many of the minicomputers of the 1970s: it provided fast 4-bit arithmetic and logic functions, and could be combined to handle larger words, making it a key part of many CPUs. But if you look at the chip more closely, there are a few mysteries. It implements addition, subtraction, and the Boolean functions you’d expect, but why does it provide several bizarre functions such as “A plus (A and not B)”? And if you look at the circuit diagram (below), why does it look like a random pile of gates rather than being built from standard full adder circuits. In this article, I explain that the 74181’s set of functions isn’t arbitrary but has a logical explanation. And I show how the 74181 implements carry lookahead for high speed, resulting in its complex gate structure.

More details at Ken Shirriff’s blog.

Analyzing the vintage 8008 processor from die photos: its unusual counters


Ken Shirriff writes:

The revolutionary Intel 8008 microprocessor is 45 years old today (March 13, 2017), so I figured it’s time for a blog post on reverse-engineering its internal circuits. One of the interesting things about old computers is how they implemented things in unexpected ways, and the 8008 is no exception. Compared to modern architectures, one unusual feature of the 8008 is it had an on-chip stack for subroutine calls, rather than storing the stack in RAM. And instead of using normal binary counters for the stack, the 8008 saved a few gates by using shift-register counters that generated pseudo-random values. In this article, I reverse-engineer these circuits from die photos and explain how they work.

More info at Ken Shirriff’s blog.

Reverse-engineering the surprisingly advanced ALU of the 8008 microprocessor


Ken Shirriff has written an article on reverse engineering the ALU of the 8008 microprocessor:

A computer’s arithmetic-logic unit (ALU) is the heart of the processor, performing arithmetic and logic operations on data. If you’ve studied digital logic, you’ve probably learned how to combine simple binary adder circuits to build an ALU. However, the 8008’s ALU uses clever logic circuits that can perform multiple operations efficiently. And unlike most 1970’s microprocessors, the 8008 uses a complex carry-lookahead circuit to increase its performance.
The 8008 was Intel’s first 8-bit microprocessor, introduced 45 years ago.1 While primitive by today’s standards, the 8008 is historically important because it essentially started the microprocessor revolution and is the ancestor of the x86 processor family that are probably using right now.2 I recently took some die photos of the 8008, which I described earlier. In this article, I reverse-engineer the 8008’s ALU circuits from these die photos and explain how the ALU functions.

More details at righto.com.

Inside the 74181 ALU chip: die photos and reverse engineering


A detailed die photos and reverse engineering of the 74181 ALU chip by Ken Shirriff:

What’s inside a TTL chip? To find out, I opened up a 74181 ALU chip, took high-resolution die photos, and reverse-engineered the chip.1 Inside I found several types of gates, implemented with interesting circuitry and unusual transistors. The 74181 was a popular chip in the 1970s used to perform calculations in the arithmetic-logic unit (ALU) of minicomputers. It is a moderately complex chip containing about 67 gates and 170 transistors3, implemented using fast and popular TTL (transistor-transistor logic) circuitry.

More details at Ken Shirriff’s blog.

Die photos and analysis of the revolutionary 8008 microprocessor, 45 years old


Ken Shirriff has written an article detailing die photos of the vintage Intel 8008 that reveal the circuitry it used:

Intel’s groundbreaking 8008 microprocessor was first produced 45 years ago.1 This chip, Intel’s first 8-bit microprocessor, is the ancestor of the x86 processor family that you may be using right now. I couldn’t find good die photos of the 8008, so I opened one up and took some detailed photographs. These new die photos are in this article, along with a discussion of the 8008’s internal design.
The photo above shows the tiny silicon die inside the 8008 package. (Click the image for a higher resolution photo.) You can barely see the wires and transistors that make up the chip. The squares around the outside are the 18 pads that are connected to the external pins by tiny bond wires. You can see the text “8008” on the right edge of the chip and “© Intel 1971” on the lower edge. The initials HF appear on the top right for Hal Feeney, who did the chip’s logic design and physical layout. (Other key designers of the 8008 were Ted Hoff, Stan Mazor, and Federico Faggin.)

More details at Ken Shirriff’s blog.

Inside a RFID race timing chip: die photos of the Monza R6


Ken Shirriff took some die photos of the Monza R6 chip  and wrote a post on his blog on how the RFID timing chip works:

I recently watched a cross-country running race that used a digital timing system, so I investigated how the RFID timing chip works. Each runner wears a race bib like the one below. The bib has two RFID tags, consisting of a metal foil antenna connected to a tiny RFID (radio-frequency identification) chip. At the finish line, runners pass over a pad that reads the chip and records the finish time. (I’m not sure why there are two RFID tags on each bib; perhaps for reliability of detection.)
The die photo below shows the RFID chip used on these tags. To create it, I took 22 photos of the chip with my metallurgical microscope and stitched them together to create a high resolution photo. (Click the image for a larger version.) To prepare the chip, I removed it from the plastic carrier with Goof Off, dissolved the antenna with pool acid (HCl), and burnt off the mounting adhesive over a stove. This process left the chip visible with just a bit of debris that wouldn’t come off. I’d probably get better results with boiling sulfuric acid, but that’s too hazardous for me. I described the image stitching process in this article.

More details at Ken Shirriff’s blog.