Enjoy retro computing with the Zeal 8-bit computer. It's fully tested, fully functional, and ready for fun!

The documentation is now public, check it out at http://docs.zeal8bit.com

The project Zeal 8-bit computer is a modern 8-bit computer made out of brand new and active components, no obsolete parts. It is powered by a real Z80 processor, not a microcontroller, nor an emulator.

The goal of this project is to have a simple, yet powerful, 8-bit computer, capable of outputting graphics, that can be used to learn about electronics, and low-level programming. It can be programmed in assembly, thanks to any Z80 assembler, and in C, thanks to SDCC. More languages support are coming.

This edition is made for developers, who are eager to port or develop software to Zeal 8-bit Computer. Indeed, its operating system, Zeal 8-bit OS, is still work in progress. Feel free to take part into the development, the community is getting bigger!

As you may have seen in the Youtube videos about the project, the final goal is also to have a video board, powered by an FPGA to have a graphical VGA output supporting text mode and graphic mode. The board is already available and you can get it on its Tindie page!

Check the Getting Started

What is included?

This product includes a pre-assembled, pre-flashed and pre-tested Zeal 8-bit Computer motherboard. A The exhaustive list of the components is:

• Z80 CPU
• Z80 PIO
• 512KB of RAM
• 256KB of NOR Flash
• 32KB of I2C EEPROM
• I2C RTC, with its crystal oscillator and a CR2025 battery (battery not included)
• 2x 4-by-4 register file (MMU/Memory mapper)
• Voltage supervisory chip (MCP)
• Programmable Logic Device for logic decoding/mapping (GAL/ATF16V8B)
• Logic chips for glue logic
• 10MHz oscilaltor
• Reset & power switches
• Jumpers and caps for configuration
• 1A fuse in its socket
• PS/2 port
• 50-pin extension port
• 16-pin user port
• USB type-C port for power input

Note 1: All the components in PLCC and DIP format are socketed, then can be put in and taken out without soldering/desoldering.

Note 2: The ROM will be preflashed with the bootloader described below, usable through UART. A USB-to-TTL/USB-to-UART adapter is required.

What is NOT included?

The following components are not included and are necessary to use the board:

• Zeal 8-bit Computer Video Card. This FPGA-based video board is not included, you can get it here.
• A 5V adapter and USB-C cable, needed to power on the board. Any phone charger and USB Type-C cable can be used for this, make sure it outputs a stable 5V voltage.
• USB-to-UART adapter. The motherboard provides TX and RX pins, you must connect a cables from there to a USB-to-TLL/USB-to-UART adapter in order to have access to the monitor.

Specifications

Here are the features of the board:

Memory Mapping

As specified in the previous section, Zeal 8-bit Computer is composed out of a 256KB ROM (NOR flash), and 512KB of RAM. However, the Z80 CPU is only capable of accessing 64KB at once. In fact, the physical memory space is 4MB big on the board, thus, Zeal 8-bit Computer provides an MMU/Memory mapper, which lets the user choose which part of the physical mapping should be accessible by the CPU. This diagram shows an example of how the virtual memory can be configured.

Around 3MB of physical memory are available to the user for potential extensions. The whole CPU bus, including but not limited to 22-bit address, 8-bit data, RD/WR, INT, MREQ, IOREQ signals are available on the 50-pin extension port, which can be used to plug external cartridges or any other type of devices.

Extensions

The board presents 3 main ports for extensions:

• 16-pin user port, which gives access to the internal I2C bus, the UART TX and RX lines, and 8 GPIOs which are directly connected to the Z80 PIO.
• 50-pin extension port which gives access to the whole CPU bus, including some extra signals such as IEI and IEO which cna be used to daisy-chain Zilog devices with the already-present PIO.
• 40-pin video card connector, which is currently NOT populated as Zeal 8-bit Video Card is still under development. Just like the extension port, it presents the main CPU signals, including the 22-bit address and the 8-bit data lines.

Software support

Thanks to this flexible memory mapping composed of 4x16KB virtual pages, the computer is compatible wih a large variety of softwares/systems, including Zeal 8-bit OS and CP/M.

A bootloader will be provided and pre-flashed on the ROM in order to let you:

• Have a multi-boot capability. (select the OS to boot on startup)
• Flash files, sent through UART, to the ROM.
• Boot programs, sent through UART, directly on the board, without the need to flash it.
• Test the hardware

Moreover, Zeal 8-bit OS latest version will also be provided on the ROM, which can be booted from the bootloader. You can learn more about it in this video.

Why this project?

The Z80 is a very old processor that had a lot of success in the late 70s and 80s. In fact, it is still manufactured and sold today! As I have always wanted to have a simple yet powerful 8-bit computer, I decided to create my own one year, in 2021. This is when this project started. The goal is to have a standalone 8-bit computer that can output text and graphics at a decent resolution (640x480). Moreover, it would be possible to program for it in C and assembly.

Support, questions and community

The project has already gathered a community of more than 100 people in the Discord server. Feel free to join the community to get support, to propose some ideas, to help with the software or simply to discuss with people passionate about retro-computing and Zeal 8-bit computer.

Join the community on:

Youtube: https://www.youtube.com/@zeal8bit

Discord: https://discord.gg/CtyGsSkzDY

Github: https://github.com/Zeal8bit

Twitter: https://twitter.com/zeal8bit