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

The ZX Spectrum’s Uncommitted Logic Array (ULA) was the "secret sauce" that made Sir Clive Sinclair’s most famous machine both affordable and iconic. Designing a retro-style microcomputer today—especially a portable one—requires understanding how this single chip managed everything from video generation to keyboard scanning. 🧠 The Heart of the Machine: What is the ULA?

The Heart of the Machine: The ZX Spectrum ULA and Retro Microcomputer Design The ZX Spectrum’s Uncommitted Logic Array (ULA) was

ULA functions — a concise breakdown

• Video generation: Generated sync signals, pixel clock, and read DRAM to form a composite video signal. It produced a 256×192 bitmap with an 8×8 attribute grid for color information.
• DRAM refresh and contention: Performed memory refresh cycles and enforced contention rules with the Z80 CPU — CPU accesses during certain phases were delayed or slowed.
• I/O control: Scanned the keyboard matrix, managed tape interface timing, and implemented simple port decode logic for the CPU’s IN/OUT instructions.
• Address mapping: Mapped ROM and RAM into the Z80 address space, with some later models supporting paging for expanded RAM.

The Retro Portable Project: Modernizing the ULA

So, how does this history lesson help you build a "portable retro computer"? Video generation: Generated sync signals, pixel clock, and

Here’s a feature overview for a retro-inspired portable microcomputer based on the ZX Spectrum ULA design philosophy: The Retro Portable Project: Modernizing the ULA So,

Since original Ferranti ULA chips were hard to find, he decided to use a modern CPLD (Complex Programmable Logic Device) to mimic the old silicon's logic [4]. The Screen: Instead of a heavy CRT television, he wired up a 3.5-inch used for car backup cameras. He swapped the bulky power brick for a Lithium-Polymer battery

Step 4: Video – From ULA to LCD

The original ULA spits out a 15.625kHz horizontal sync (PAL). A modern LCD expects 31kHz (VGA) or 74.25MHz (HDMI).