Post #1456252

2026-04-17 19:09 UTC

Hi! A little bit late in the day, but #nakeddiefriday is still happening today. And today&#39;s exhibit is TC8568AM by Toshiba. This is a VFO to be used in floppy disk controllers. This is made very prominent on the die itself. Interesting how such a discrete part was still made in early 90s, where I kind of expected them to be replaced by fully integrated parts. A really short thread will follow. Full-res map: http://infosecdj.net/map/toshiba/tc8568am/infosecdj_mz_nikpa40x_66p/ Many thanks to @RueNahcMohr for supplying this sample! #electronics #reverseengineering #microscopy

Replies (4)

@infosecdj@infosec.exchange 2026-04-17 19:16

In the bottom left corner we have what looks like a die ID (D930 0001A) along with e-test features. These are two transistors with a common gate wire, which apparently has an ESD protection diode as well.

Open ##1581437
@muddle@infosec.exchange 2026-04-18 00:13

@infosecdj @RueNahcMohr This piqued my interest and got me wondering why a VFO (variable-frequency oscillator) would be used in a floppy controller. From what I guessed/researched, it seems that data tracks on the floppy surface are encoded at a fixed density. This would mean that tracks closer to the centre have less data compared to the outer tracks. Assuming a constant (or near-constant) angular speed, data from different tracks would be arriving at different rates. Based on this, the VFO has two purposes: synchronise a phase-locked loop to the particular track speed (based on special track markings)report the speed back to the controller so that it can read data at the correct rate That's really as far as I researched it. It may also be that finer adjustments to the data rate might happen during a track read? That would probably depend on the particular disk format and encoding used. I think the above is OK to a certain level of approximation. Please let me know if I'm wildly off the mark.

Open ##1581445
@RueNahcMohr@infosec.exchange 2026-04-18 06:28

@infosecdj Ooo I will have to look for more of those!....

Open ##1581451
@brouhaha@mastodon.social 2026-04-18 08:43

@infosecdj @RueNahcMohr There must be more to that chip than a VCO. There's way more circuitry than a VCO needs. Maybe it's an entire data separator?

Open ##1581452