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

Integrate a small 3.5-inch or 5-inch TFT LCD panel inside your custom chassis. Step 3: Power and Portability

The true art of here is re-timing . The original Spectrum relied on a 14.218MHz master crystal (4x the 3.5469MHz pixel clock). For a portable with an LCD, you don’t need a PAL TV signal. You can generate 60Hz VGA or HDMI, but you must maintain 100% timing compatibility with the Z80 software. This is the "ULA replacement" problem.

. It had to constantly "steal" time from the Z80 processor to draw the screen, a delicate dance called contended memory

It handled the scanning of the 40-key matrix keyboard, managed the cassette tape input/output lines, and generated audio for the internal beeper speaker.

The ULA, also known as the Ferranti FDC 6670, was a custom-designed chip created by Ferranti for Sinclair Research. This chip combined various functions, including: Integrate a small 3

The classic Spectrum keyboard is a membrane matrix that feels uniquely rubbery. For a modern portable computer:

This is the most efficient path for a handheld device, requiring only a few custom PCBs to house the microcontroller, a battery, and a tactile keyboard. Raspberry Pi Technical Resources for Designers

+-------------------------------------------------------+ | PORTABLE MICROCOMPUTER | | | | +-------------------+ +---------------------+ | | | Z80 CPU | | FPGA / CPLD (ULA) | | | | (Physical/Core) |<=====>| - Video Generation | | | +-------------------+ | - Keyboard Matrix | | | | - Contention Logic | | | +-------------------+ +----------+----------+ | | | SRAM / ROM | | | | | (System RAM) |<-----------------+ | | +-------------------+ v | | +---------------------+ | | +-------------------+ | TFT/LCD DISPLAY | | | | Li-ion Battery & | | (RGB/SPI Drive) | | | | Power Management | +---------------------+ | | +-------------------+ | +-------------------------------------------------------+ Step 1: Choosing Your Core Processing Unit You have two primary routes for the CPU:

Filter the digital 1-bit audio output pin from your ULA logic through a low-pass RC filter before feeding it into a class-D headphone amplifier. For a portable with an LCD, you don’t need a PAL TV signal

Use a standard Lithium-Polymer (LiPo) or 18650 battery cell .

Your HDL code must implement a global horizontal and vertical counter. For a standard PAL display:

To design a portable microcomputer inspired by the ZX Spectrum, you must first master the original ULA's architecture. Built by Ferranti using a 600-gate Uncommitted Logic Array, this single chip replaced roughly 40 discrete TTL integrated circuits, allowing Sinclair to achieve an unprecedented low price point. 1. Video Generation and Timing

Fully tactile 40-key matrix keyboard tailored for classic Sinclair keyword shortcuts. but rather efficient

to emulate the Z80. This is easier for portable builds as it handles power management better. 2. Replacing the ULA

An FPGA (e.g., Lattice iCE40 UP5K or Sipeed Tang Nano) can replicate the ULA’s parallel logic exactly.

Finally, the ULA symbolizes the ethos of the "home computer" era: accessibility through efficiency. Clive Sinclair wanted a computer that could fit into a briefcase and sell for under £100. The ULA was the engine of that democratization. Today, the "portable retro computer" market is booming, driven by devices like the Raspberry Pi Zero or dedicated FPGA handhelds. These devices owe their existence to the design philosophy proven by the ULA—that the soul of a computer does not require a massive chassis, but rather efficient, integrated logic.

3.5" to 5" TFT LCD panel supporting crisp integer scaling.

Original microcomputers relied on power-hungry, inefficient linear regulators (like the LM7805) that generated significant heat. For a portable design: