Foreword

❤️ Thank you for buying the Zeal 8-bit Computer !

You have obtained more than just an 8-bit computer. You have received an invitation to join a new community.

For the past few decades, computers have been getting more and more powerful, with increasing numbers of transistors, components, capabilities and features, all while getting more affordable and usable by the general public.

But with all these technological advances came something else that was unavoidable: complexity.

Today, computers tend to be so complex that they cannot be completely understood by a single person. They have become black boxes, with many of their inner workings undocumented or intentionally hidden behind proprietary interfaces.

What's the problem with this? For most people, interacting with the operating system and running typical software like games, web browsers, and text editors is all they desire to know about their computers. But what about all those people who are curious to understand these machines at a deep level, the inner workings of the operating system, the low-level code that interfaces the hardware, and the hardware itself?

These people are often told to learn a low-level programming language like C, or to start programming on an embedded platform such as a Raspberry Pi, and Arduino, or an ESP32 microcontroller. These embedded devices present less complexity than a modern desktop computer, but they are still far too complex to completely understand how they work at every level. The Raspberry Pi for example hides much of it's low-level code behind proprietary firmware which is not open to the public to view and understand.

It is with all this in mind that we started designing the Zeal 8-bit Computer in early 2021. The main goal of the project is to have a computer that can execute any code (games or any other software) while being simple enough to master and be fully understood at every level. A single person should be able to understand this system from the hardware layer all the way up through the operating system's internal structure.

As a starting point, the computer is based on an 8-bit processor, the Zilog Z80, that has been commercially available since 1976. Unlike a microcontroller, the Z80 doesn't embed any ROM, RAM, GPIO or even UART. This processor has a single role: fetch and execute instructions. Thus, it is a perfect candidate for the project!

Built around this processor is all the supporting hardware needed for a complete system: ROM, RAM, I/O ports, address and data buses, etc. These discrete sub-systems are well documented and can be understood by a single person. Instead of a "back box", you can think of this design as a "white box".

Each component that comprises the Zeal 8-bit Computer has a single role. In this manual we will explain how each component works and how they interact with each other. We will also learn how we can extend the computer to add more features.

🚀 Let's get started