I recently came across an interesting die photo of a Soviet1 chip, probably designed in the 1970s. This article provides an introductory guide to reverse-engineering CMOS circuits, using this chip as an example. Although the chip looks like a tangle of lines at first, its large features and simple layout make it possible to understand its circuits. I'll first explain how to recognize the individual transistors. Groups of transistors are connected in standard patterns to form CMOS gates, multiple...