In the early 1980s, custom ASICs (Application-Specific Integrated Circuits) were expensive. Sinclair Research, always pushing the boundaries of affordability, turned to Ferranti to use their ULA technology.
From a design perspective, the ULA represented a pivot toward "system-on-a-chip" thinking long before the acronym became an industry standard. For the modern designer building a portable retro computer, the lessons of the ULA are vital. The primary constraint in portable design is real estate. A modern handheld cannot accommodate the sprawling PCBs of 1980s originals. Designers today often use CPLDs (Complex Programmable Logic Devices) or FPGAs (Field-Programmable Gate Arrays) to mimic the behavior of the original ULA. By replicating the ULA’s logic in a modern FPGA, a designer can reproduce the Spectrum’s video output and memory banking while shrinking the hardware footprint to the size of a postage stamp. For the modern designer building a portable retro
FPGAs allow for enhancements like VGA/HDMI output, SD card storage for instant game loading, and even "ULAPlus" for expanded color palettes. No-ULA Design: Some hobbyists, featured on Designers today often use CPLDs (Complex Programmable Logic
For beginners, an RP2040-based emulated version is faster to prototype. But for the true “design a microcomputer” experience—understanding contention, video timing, and memory arbitration—an FPGA ULA is the definitive modern method. No-ULA Design: Some hobbyists
[Z80 CPU] <-- data/addr/control bus --> [RP2040 (acting as ULA + RAM + ROM)] | +---> [Small SPI LCD (ST7789)] +---> [SD card (for .tap/.z80 files)] +---> [Beeper amplifier + speaker] +---> [Li-ion charger + 3.3V LDO] +---> [USB-C (power + HID)]
: The author exposes the inner workings of the ULA in minute detail, featuring over 140 illustrations and circuit diagrams.