CoBra XP: The Ultimate Z80 Experimentation Platform

Introducing CoBra XP, a Z80-based computer design derived from the legendary Cobra project. This project is a tribute to the dedicated modding community that has worked tirelessly to expand the capabilities of their Cobra computers. 

Through track cutting, wiring, and extension boards, they’ve pushed the limits of what’s possible. Now, CoBra XP continues this tradition by offering a robust platform for experimenting with digital circuits and creating new Z80 projects.

A Playground for Hardware Experimentation

CoBra XP isn’t just another Z80 board; it’s a system designed for exploration and learning. Whether you’re an experienced modder who knows PCB schematics inside and out, or a beginner looking for a serious challenge, this project has something to offer.

That said, this isn’t a plug-and-play project—it requires knowledge, patience, and a passion for debugging. If you love the thrill of troubleshooting and optimizing your build, this is the perfect playground for you!

Experiment Status: First Boards Are Here!

A batch of 10 CoBra XP mainboards has already arrived, with one successfully booting in a 64K configuration. The community is actively testing and refining the system, making it an exciting time to join the project.

Technical Specifications

Here’s a breakdown of what makes CoBra XP special:

• CPU: Z80A running at 3.5MHz

• Memory: Two banks of 16-pin DRAM chips (supports 4164 or 5V-only 16Kbit DRAM like MCM4517)

• Memory Modes: Three different configurations: Boot mode, CP/M mode, ZX Spectrum mode

• ROM Options: Supports 27C128, 27C256, 27C512, and 28C256 (28-pin)

• BASIC Interpreter ROM: Uses a 32-pin socket, supporting up to 4Mbit 39SF040 ROM (8 selectable 16KB pages)

• Video Interface: ZX Spectrum-style 256 x 192 resolution with a relocatable base address

• Keyboard: 58-key layout (50 keys for ZX Spectrum mode + 8 for CP/M mode)

• Sound: AY39810 sound chip for rich audio capabilities

• Storage: i8272 floppy interface (daughterboard required, not yet in repo)

• Connectivity:

  • RS232 port (bit-banged through 8255)

  • Joystick port

  • Prototyping area with a PLCC 84 THT socket

  • Five unpopulated 28-pin DIP footprints (for additional GAL chips)

  • Six 10-pin headers + one 4-pin for power, all connected to address/data buses

  • Expansion support through a 3x32 pin DIN41612 connector

  • Multiple test points for easier debugging

  • SMD jumpers for circuit modifications

Built for Modders and Innovators

What sets CoBra XP apart is its mod-friendly design. The PCB includes multiple test points for address and data buses, as well as GND points for hooking up oscilloscope probes. Additionally, smd jumpers allow for custom modifications, making this an ideal board for hardware experimentation.

For those looking to expand CoBra XP, daughterboard extensions can be easily created thanks to aligned headers designed for perfboard compatibility. A template for custom expansions is also available in the repository.

Ready to Experiment?

CoBra XP is more than just a retro computing project—it’s a journey into the heart of digital circuit design. Whether you want to build a custom Z80 computer, develop new software for CP/M, or push the limits of ZX Spectrum emulation, this platform is an excellent choice.

Just remember: this is an experiment, not a finished product. Expect challenges, enjoy the debugging process, and be part of a growing community pushing the boundaries of Z80 computing.

Check out the official repository for more details: CoBra XP on GitHub