The Zx Spectrum Ula How To Design A Microcomputer Zx Design Retro Computer Portable Online
Here’s a feature overview for a retro-inspired portable microcomputer based on the ZX Spectrum ULA design philosophy:
Happy building, and remember – every cycle counts when you're stealing them from the Z80
The "ULA" Legacy in Your Pocket
The philosophy of the ULA—integrating complex systems into a single chip—is exactly what powers our smartphones today. The System-on-Chip (SoC) in your pocket is the great-great-grandchild of the Ferranti ULA. Here’s a feature overview for a retro-inspired portable
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.
Retro Computer and Portable Design
The ULA taught Sinclair how to design a microcomputer on a shoestring. Now, it will teach you how to build a retro computer portable that fits in your backpack. The ghosts of 1982 are waiting for your solder smoke.
The Sinclair ZX Spectrum wasn't just a computer; it was a masterclass in minimalist design. Central to its magic was the ULA (Uncommitted Logic Array)—a single custom chip that replaced dozens of standard components. This was the "secret sauce" that made the Spectrum affordable, compact, and eventually portable. FPGA: Small mid-range part (e
3) Building blocks and components
- FPGA: Small mid-range part (e.g., Lattice iCE40 or ECP5) depending on HDMI needs (ECP5 recommended for HDMI).
- Z80: Z84C0006 or equivalent if using discrete CPU; alternative: T80/Z80 soft core.
- DRAM: 8-bit SDRAM or classic DRAM chips (e.g., 4116/4164 emulation via SDRAM controller). Use modern SDRAM with FPGA controller.
- Flash/ROM: SPI NOR for firmware; microSD socket for images.
- Power: USB-C PD or 5V regulator with Li-ion charger IC (e.g., MCP73831 or better).
- Display: 5–7" SPI or MIPI LCD, driven by an MCU/FPGA bridge.
- Codec: Audio via DAC or PWM filtered to resemble beeper/tape sounds.
- Peripherals: 3.5 mm joystick, USB HID bridge, GPIO headers.
| Function | Description | |----------|-------------| | Video Generation | Produces 15.625 kHz horizontal and 50 Hz vertical sync (PAL). Outputs 256×192 pixels, 1-bit per pixel, with attribute clash. | | Memory Arbitration | Interleaves Z80 access and video fetch during the 6.5 MHz clock. CPU runs at ~3.5 MHz but is halted during video display (contended memory). | | I/O Decoding | Decodes port 0xFE for keyboard reading, sound (beeper), and cassette mic/ear. | | DRAM Refresh | Provides RAS/CAS timing for 4116-style DRAMs. | | Clock Generation | Divides a 14.21818 MHz master clock down to 3.5469 MHz (Z80) and pixel clock. |