decap

15 Articles

The Intel 8087 And Conditional Microcode Tests

January 11, 2026 by 19 Comments

Continuing his reverse-engineering of the Intel 8087, [Ken Shirriff] covers the conditional tests that are implemented in the microcode of this floating point processing unit (FPU). This microcode contains the details on how to perform the many types of specialized instructions, like cos and arctan, all of which decode into many microcode ops. These micro ops are executed by the microcode engine, which [Ken] will cover in more detail in an upcoming article, but which is effectively its own CPU.

Conditional instructions are implemented in hardware, integrating the states of various functional blocks across the die, ranging from the instruction decoder to a register. Here, the evaluation is performed as close as possible to the source of said parameter to save on wiring.

Implementing this circuitry are multiplexers, with an example shown in the top die shot image. Depending on the local conditions, any of four pass transistors is energized, passing through that input. Not shown in the die shot image are the inverters or buffers that are required with the use of pass transistors to amplify the signal, since pass transistors do not provide that feature.

Despite how firmly obsolete the 8087 is today, it still provides an amazing learning opportunity for anyone interested in ASIC design, which is why it’s so great that [Ken] and his fellow reverse-engineering enthusiasts keep plugging away at recovering all this knowledge.

As Cheap As Chips: The MiFare Ultra Light Gets A Closer Look

June 26, 2024 by 8 Comments

If you take public transport in many of the world’s cities, your ticket will be an NFC card which you scan to gain access to the train or bus. These cards are disposable, so whatever technology they use must be astonishingly cheap. It’s one of these which [Ken Shirriff] has turned his microscope upon, a Montreal Métro ticket, and his examination of the MiFare Ultra Light it contains is well worth a read.

The cardboard surface can be stripped away from the card to reveal a plastic layer with a foil tuned circuit antenna. The chip itself is a barely-discernible dot in one corner. For those who like folksy measurements, smaller than a grain of salt. On it is an EEPROM to store its payload data, but perhaps the most interest lies in the support circuitry. As an NFC chip this has a lot of RF circuitry, as well as a charge pump to generate the extra voltages to charge the EEPROM. In both cases the use of switched capacitors plays a part in their construction, in the RF section to vary the load on the reader in order to transmit data.

He does a calculation on the cost of each chip, these are sold by the wafer with each wafer having around 100000 chips, and comes up with a cost-per-chip of about nine cents. Truly cheap as chips!

If NFC technology interests you, we’ve taken a deep dive into their antennas in the past.

A Classy SDR Chip, Decapped

May 27, 2018 by 20 Comments

If you are a regular searcher for exotic parts among the virtual pages of semiconductor supplies catalogs, you will have probably noticed that for a given function it is most often the part bearing the Analog Devices logo that is the most interesting. It may have more functionality, perhaps it will be of a higher specification, and it will certainly have a much higher price. [Zeptobars] has decapped and analyzed an AD chip that holds all three of those honors, the AD9361 SDR transceiver.

It’s placed under a slightly inflammatory title, “when microchips are more profitable than drugs“, but does make a good job of answering why a semiconductor device at the very cutting edge of what is possible at the time of release can be so expensive. The AD9361 is an all-in-one SDR transceiver with an astonishing bandwidth, and as such was a particularly special device when it reached the market in 2013. We see some particularly fine examples of on-chip inductors and PLL circuitry that must have consumed a significant design effort to preserve both bandwidth and noise characteristics. This is an item of physical beauty at a microscopic scale as well as one of technical achievement.