A 1960s logic chip gets a digital autopsy

A rare Signetics ST680a integrated circuit, a quad-NAND gate built with diode-transistor logic (DTL) and housed in one of the earliest plastic dual in-line packages (PDIP), has been meticulously reverse-engineered. This chip represents a transitional technology from the mid-1960s, used before transistor-transistor logic (TTL) became the dominant standard due to its superior speed and power efficiency.

Analyzing this chip provides a tangible snapshot of semiconductor engineering history, showing the simpler diode-based gate design that was a mature, well-understood technology before TTL was perfected. The effort to physically decap the plastic package to expose and document the silicon die preserves knowledge of a nearly extinct logic family, offering engineers and hobbyists a fascinating look at the incremental progress that built modern computing.