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The ZX Spectrum ULA was designed by Ferranti, a renowned British electronics company, in collaboration with Sinclair Research Ltd. The ULA was fabricated using a 5 μm CMOS process, which was quite advanced for its time. The chip contains approximately 15,000 transistors and operates at a clock frequency of 3.5 MHz.
Ferranti produced the ULA using a "diffusion programming" technique. Unlike a mask ROM or a gate array, the ULA started as a standard base wafer of unconnected gates. The final metal layer was customized via a computer-controlled electron beam. The ZX Spectrum ULA was designed by Ferranti,
Steve Vickers, the mathematician tasked with writing the ROM (Read-Only Memory) software, walked into the lab one afternoon. "The machine keeps crashing when I try to draw a circle in high-res mode," Vickers said, holding a circuit board. Ferranti produced the ULA using a "diffusion programming"
, a precursor to modern FPGAs. It was a "blank slate" of logic gates that could be custom-wired at the factory to replace nearly all the support circuitry of a microcomputer in one single chip. Core Functions: The ULA’s Busy Schedule Steve Vickers, the mathematician tasked with writing the