Recreating the ZX Spectrum experience hinges on reproducing both function and timing. Using an FPGA to implement a modern ULA lets you preserve the machine’s behavioral quirks (what made the Spectrum special) while adding modern conveniences for portability. Start with a focused FPGA video/DRAM prototype, iterate with a simple ROM and Z80 core, and build outward—balancing authenticity and usability to produce a compact, lovable retro microcomputer.
Implement the Logic (The ULA Replacement)For an authentic hardware feel, use a CPLD (Complex Programmable Logic Device) or FPGA. These chips can be programmed to behave exactly like the Ferranti ULA. If you prefer a software-defined approach, a high-speed microcontroller can "bit-bang" the video signal and manage memory timings. Recreating the ZX Spectrum experience hinges on reproducing
It read data from the "lower" RAM (0x4000 to 0x7FFF) to generate the raster signal for television sets. Memory Contention: Implement the Logic (The ULA Replacement)For an authentic
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Smith explains the origin of famous hardware "bugs," such as the "Snow Effect" (caused by memory contention) and the non-standard composite sync pulses that many modern TVs struggle to process. It read data from the "lower" RAM (0x4000