module ula( input clk_14M, input nRST, inout [7:0] data_bus, input [15:0] address, output nWAIT, output nINT, output composite_video );
18;write_to_target_document1b;_XGrtac6NMbbz4-EP_-fH0Qk_100;57; 0;bd3;0;5e9; 0;11c5;0;21d1; The ZX Spectrum ULA: How to design a microcomputer
The ZX Spectrum ULA: Designing a Retro Microcomputer The (Uncommitted Logic Array) is widely regarded as the "heart" of the Sinclair ZX Spectrum. Originally manufactured by Ferranti , this custom gate array consolidated nearly all the discrete logic required to build a functional microcomputer into a single silicon chip . Understanding its design is essential for any hobbyist or engineer interested in retro-style computing or modern hardware preservation. module ula( input clk_14M, input nRST, inout [7:0]
The ULA continuously reads data from the video memory area in the lower RAM (addresses 0x4000 to 0x7FFF ). It decodes pixel bytes and attribute bytes (which control foreground and background colors) and serializes them into video signals. It also generates the video border color dynamically. 2. RAM Contention Handling
If you are planning to build your own, are you considering an or a more traditional discrete logic approach ? I can provide more technical details on the memory map or contention timing if you'd like to dive deeper. The ULA continuously reads data from the video
: Details the "contention" that occurs when both the CPU and ULA attempt to access the lower 16K of RAM simultaneously. I/O Handling
Sir Clive Sinclair’s philosophy was radical cost reduction. The solution was the ULA, manufactured by Ferranti. It combined roughly 1500 individual logic gates onto a single piece of silicon, shrinking a massive circuit board into one 40-pin chip. Core Architectural Responsibilities of the ULA the computer was e-waste.
Modern approach: Write this in VHDL/Verilog for a CPLD or use an RP2040 with PIO state machines.
Smith’s 324‑page volume, published in 2010, exposes the inner workings of the Spectrum’s custom chip for the first time, revealing the design decisions that turned a simple Z80 CPU into one of the most successful home computers of the 1980s. With more than 140 illustrations and circuit diagrams, the book is simultaneously a technical dissection of the Ferranti ULA and a hands‑on guide to the principles and techniques needed to design an 8‑bit microcomputer from scratch. It is aimed at electronics hobbyists, students and engineers who wish to create their own retro‑style computer — or simply to understand what made the Spectrum tick.
If the ULA died, the computer was e-waste. This was the antithesis of the Apple II (which had socketed TTL chips). This trade-off (unrepairable vs. affordable) defined the British home computer boom.
Monitoring the 40-key membrane keyboard for input. Audio Output: Producing the "beeper" sound.