In the fast-paced world of modern computing, there's something deeply grounding about going back to the roots—back to when computers were machines you could touch, understand, and even build yourself on a kitchen table. While today's processors contain billions of transistors hidden behind layers of abstraction, the Z80 microprocessor from the 1970s remains a beloved gem among hobbyists. Simple, reliable, and historically significant, the Z80 and its many clones continue to inspire hands-on exploration of computing’s foundations.

This project is about creating a simple, working Z80 microcomputer using the LH0080AZ80A-CPU-D, a clone of the legendary Zilog Z80. No modern coding platforms, no operating systems—just raw hardware, wires, and patience. The goal is not to create a high-performance machine, but to build something tangible: a living, breathing computer that lights up, responds, and makes you feel like you've built your own piece of history.

Why the LH0080AZ80A-CPU-D?

Before diving into the project, it’s worth understanding why we’re using this particular component. The LH0080AZ80A-CPU-D is a NEC-produced clone of the original Zilog Z80. It’s fully compatible, pin-for-pin, with the Z80A, which means it can run the same instructions, interface with the same memory, and be used in virtually any classic Z80 circuit.

It’s a DIP (dual in-line package) chip, which means it’s breadboard- and socket-friendly—perfect for prototyping. It’s also power-efficient, runs at moderate speeds (typically 4MHz to 8MHz), and can be sourced from vintage suppliers or auctions relatively easily.

This chip represents an era when processors were understandable and approachable. And for our purposes, it’s the heart of the DIY microcomputer we’re about to bring to life.

The Project: A Minimal Z80 Homebrew Computer

This isn’t going to be a recreation of an old CP/M machine or a full terminal-ready computer with video output. Instead, we’ll be creating a bare-bones microcomputer: a simple, functioning Z80 system that boots up, executes instructions from ROM, and allows for user interaction via LEDs and switches.

It’s like building a campfire in the age of central heating—not strictly necessary, but deeply satisfying.

The Vision

At the end of this project, you’ll have a small computer on your desk that powers on, starts executing instructions from a ROM chip, and interacts with you through basic input/output—such as blinking LEDs or reacting to DIP switches. You’ll be able to reset it manually, watch the address and data buses light up as it runs, and feel a genuine connection to how machines used to work.

The whole system will be powered from a simple regulated DC supply and built mostly on a perfboard or breadboard.

The Hardware Journey

Step 1: Planning the Core System

At the heart of every computer is the processor, memory, and a clock. For our Z80 build, we start with:

● LH0080AZ80A CPU

● Static RAM (SRAM) chip, like a 6264 (8K) or similar

● EPROM or EEPROM to store a simple bootloader

● 74-series logic for decoding addresses and controlling data flow

● Clock circuit, likely a crystal oscillator or timer-based square wave

● Basic I/O: LEDs for output, switches for input

We aim to build a minimal architecture: 8K ROM, 8K RAM, basic address decoding, and some GPIO. No screens, no keyboards (yet), just the joy of seeing logic work.

Step 2: Setting Up the Clock

Every CPU needs a heartbeat. For the Z80, a clean clock signal is critical. The LH0080AZ80A runs happily at 4MHz to start with, so we wire up a small clock circuit—perhaps a simple oscillator module or a crystal-based timer.

It’s fascinating to watch the CPU come to life with just a ticking square wave. You don’t need to see software running yet—the fact that the chip is receiving a pulse, and responding to it, is the start of something magical.

Step 3: Memory Mapping

With the CPU pulsing away, we need to give it a brain and a memory. The RAM and ROM are wired directly to the data and address buses, with control signals to enable reading and writing.

We burn a simple machine language program into the ROM—nothing fancy, maybe just a loop that toggles bits on a port. The magic happens when you wire it up, power on the board, and see an LED flash. At that moment, it’s not just a pile of components—it’s a computer.

Even without code displayed here, that LED blinking is proof that the CPU is reading instructions from memory, processing them, and triggering outputs. It’s an incredible moment for any builder.

Step 4: Address Decoding

To ensure the CPU reads and writes to the correct memory areas, we implement basic address decoding using 74LS138 or similar logic chips. This lets us designate ranges for RAM and ROM, and potentially some I/O ports.

Decoding the address bus is like drawing a map of the computer's world. You say, "from 0000h to 1FFFh, that's the ROM. From 2000h to 3FFFh, that's RAM. Beyond that, we'll talk to LEDs and switches."

Suddenly, the CPU has structure—it knows where to fetch instructions, where to store temporary values, and how to reach out to the world.

Step 5: Adding Basic I/O

Here’s where it gets personal. We connect a few LEDs to output ports using a latch (like the 74LS373 or similar), and maybe some switches or DIP toggles to input ports.

This is the simplest form of interactivity: flip a switch, watch a change; see LEDs respond to internal CPU activity. Maybe the program reads an input port and lights different LEDs based on switch positions. Maybe it counts up and lights them in binary.

It’s not flashy, but it’s real. You’re watching a microprocessor think, decide, and act—all in front of your eyes, all with no layers of abstraction in between.

Step 6: Building a Reset Circuit

A manual reset circuit—often a simple push button with a pull-up resistor—lets you restart the system. It’s incredibly useful during development and experimentation. You can power-cycle the CPU without turning off your whole bench.

More importantly, pressing that reset button and watching the CPU restart its execution is a tactile reminder: this isn’t a black box. You’re the one in control.

The Experience

Working on this project is like stepping into a time machine. You’re not just learning electronics—you’re learning computing in its most primal form. You become acutely aware of every signal, every byte, and every decision the processor makes. There’s no hiding behind compilers or IDEs. It’s just you, the chips, and the raw process of building something from scratch.

You’ll spend hours tracing wires, debugging odd behaviors, and watching the buses with your multimeter. Each fix, each working segment, brings a disproportionate amount of satisfaction.

This isn’t instant gratification—it’s slow, deliberate, and deeply fulfilling.

Expanding the Build

Once the core is stable, the possibilities open up:

● Add a serial interface using a UART (like a Z80 SIO or a simpler 6850) to connect to a terminal.

● Build a keypad interface to input simple commands.

● Add a seven-segment display to show numerical output.

● Experiment with bus expansion, daisy-chaining additional memory or I/O ports.

● Implement basic ROM monitors, bootloaders, or custom instruction sequences for testing.

Every addition isn’t just an upgrade—it’s a lesson in architecture, timing, logic design, and system integration.

Lessons Learned

This project teaches more than just electronics. It offers an appreciation for the elegance of early computing, where every part mattered, and every signal was meaningful.

It teaches patience—because breadboarding a 40-pin CPU with multiple support chips is not a fast process.

It teaches humility—because even seasoned engineers will get stumped by a missed connection or an inverted control line.

But most of all, it teaches confidence. The moment you see that first LED flash in response to a sequence of binary instructions, you know you’ve built a real, functioning computer. And you did it with your own hands.

Final Thoughts

In a world obsessed with speed and efficiency, building a Z80-based microcomputer from scratch using the LH0080AZ80A-CPU-D feels like a rebellious act. It’s a return to curiosity, to the joy of understanding, and to the tactile world of blinking lights and silicon intelligence.

It’s not about what this computer can do—it’s about what you can learn by building it.

So, if you ever find yourself yearning for a deeper connection to the machines that shape our lives, take a weekend, clear your workbench, and build a little piece of history with the LH0080AZ80A. You won’t regret it.