45 years later, the Sinclair ULA design documents surface

A trove of original Ferranti Uncommitted Logic Array (ULA) design documents for Sinclair-era machines has surfaced after being bought on eBay and made available by a preservationist group. The materials include printouts, engineering drawings and handwritten notes covering the full range of Sinclair hardware from that period: the ZX81 and ZX Spectrum, the ZX printer, the Microdrive, the Spectrum Interface 1 and even the flat‑screen TV. The Ferranti ULA - an ASIC approach that bundled a library of logic cells - was central to Sinclair’s ability to deliver very low‑cost yet capable 8‑bit machines, and these files reveal internal implementations and design intent previously hidden from public view.

The archive is catalogued in a Google spreadsheet with download links and accompanied by video and a period film about Ferranti, and the current IP owner (Sky, via Amstrad’s portfolio) has permitted sharing with minimal redaction. Of particular technical interest are several ULA variants that haven’t been reverse‑engineered yet and the subtle differences between versions that document iterative bug fixes and engineering tradeoffs. The documents provide concrete schematics and notes that can accelerate accurate emulation, silicon recreation or historical research into Sinclair hardware design and manufacturing practices.