The Zx Spectrum Ula How To Design A Microcomputer Zx Design Retro Computer Portable Jun 2026

: Delaying the CPU's access to the lower 16KB of RAM when the ULA needs it for the display, leading to "contended memory" behavior.

always @(posedge clk_14m) begin if (hcount < 128) begin // 64 us fetch period mem_oe = 1; // ULA reads screen cpu_wait = 1; // Stall Z80 end else begin mem_oe = 0; cpu_wait = 0; end end : Delaying the CPU's access to the lower

The original Spectrum’s 16K or 48K of DRAM is a nightmare for portables. DRAM requires -5V, +12V, and +5V, plus constant refresh. Instead, use a single 512Kx8 SRAM chip. Instead, use a single 512Kx8 SRAM chip

Creating a portable ZX Spectrum-compatible device involves shrinking the footprint without losing the "soul" of the machine. The original design used a rubber chiclet keyboard that was notoriously difficult to type on, but essential for the Spectrum’s aesthetic. but essential for the Spectrum’s aesthetic.