Since original Ferranti chips are rare, you have three modern paths: CPLD/FPGA:
Are you currently working on a Spectrum portable build? Are you team "Original Hardware" or team "FPGA"? Let us know in the comments!
Because both the Z80 CPU and the ULA need to access the same system RAM, a conflict arises. The video generation cannot stop, or the TV screen will flicker or tear. The ULA takes absolute priority over the lower of RAM (contended memory).
Here's a pseudo-code outline for the main loop: Since original Ferranti chips are rare, you have
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.
The community has produced countless STL files for Spectrum cases: clamshell laptops, Game Boy‑style handhelds, and original wedge-shaped desktop replicas. Ensure your design includes cutouts for the screen, keyboard, SD card slot, USB port, power switch, and audio output.
Taking a Z80-based design and making it portable brings unique challenges, particularly regarding and display technology . Portable Design Considerations: Because both the Z80 CPU and the ULA
This article explores the magic of the ULA, how to design a microcomputer around it, and how to capture that retro magic in a modern portable project. 1. What is the ZX Spectrum ULA?
If you want to understand the Spectrum’s specific internal hardware architecture, the repository on GitHub provides an extremely detailed, structured breakdown of the Z80, the ULA timing, and the machine's inner workings.
pixel blocks (attributes). Each block defines the Ink (foreground), Paper (background), Brightness, and Flash status, resulting in the famous "attribute clash" artifact when moving sprites cross block boundaries. 2. Memory Contention (The "Lower 16K" Dance) Here's a pseudo-code outline for the main loop:
. It uses no custom chips, making it the perfect "manual" for how a microcomputer actually thinks. If you’d like to move forward, let me know: software emulation Are you planning to the enclosure? for a basic breadboard prototype?
The ZX Spectrum is a titan of home computing history. When it was released in 1982, it was remarkably compact, colorful, and affordable. At the heart of this success was a single, revolutionary component: the . For engineers and enthusiasts today looking to understand retro-computing design, or even build their own portable, FPGA-based ZX Spectrum, understanding the ULA is essential.
Use a Xilinx or Altera chip to recreate the ULA logic (see the project for schematics). Discrete Logic: Use 74-series chips (this results in a very large board). Microcontroller:
Armed with this knowledge, the retro computing community set about creating . Early attempts used Complex Programmable Logic Devices (CPLDs)—smaller, simpler, and cheaper than full FPGAs—to replicate the chip's behaviour. Today, FPGA-based solutions are more common, with projects like Lotharek's SLAM128 offering drop-in replacements for 128K Spectrums. These modern incarnations often add enhancements: composite and VGA output, improved sound, SD card storage and even built-in joystick ports. Some enterprising builders have gone further, recreating the Spectrum using only standard 74-series logic chips, sidestepping the ULA entirely—a popular approach among Eastern European cloners.