Bringing the Intel 8080 Back to Life

A favorite pastime of retro computing and computer engineering hobbyists involves getting vintage CPUs up and running from scratch. Whether it is a 6502, Z80, or an early Intel chip, this is an excellent way to learn more about how computers work while having some fun in the process. The first step is usually a free-run on a breadboard, in which the CPU is continually fed a NOP instruction so that it perpetually cycles through its address space sequentially.

That is enough to show that the processor is alive and kicking, and that you can manage the power and control signals, but after watching the address values count up for a few minutes, it starts to get old. Naturally, the next step is to build some type of usable computer around the chip, but that is a much bigger effort, so where do you get started?

There are any number of ways one can go at that point, but YouTuber MarkTheQuasiEngineer lays out one option in detail. He wanted to run a 50-year-old Intel 8080 CPU, and be able to interact with it and program it from a modern computer. His solution involved designing a custom system board that used all modern hardware to interface with the 8080.

The build has three primary components: an interface to a modern computer via a USB-to-UART chip, a simulated 8080 system complete with RAM, control signals, buses, and a clock signal, and finally, the 8080 itself. To handle the USB-to-UART function, an STM32 microcontroller was selected. Simulating the hardware of an 8080 system is a bit more complex, so a Microchip FPGA was utilized. That allowed MarkTheQuasiEngineer to build all the necessary components into one chip.

Between the modern hardware and the 8080, lots of different voltage levels were needed. The USB-C connection only supplies 5 volts, but 1v2, 3v3, -5 and 12 volt rails were also needed. And that meant lots of voltage level shifters, which are some of the most prominent features on the custom PCB that MarkTheQuasiEngineer designed for the project.

Once that shiny new PCB arrived, things did not work as expected. Doesn’t it always seem to go that way on the first try? But fortunately, after debugging issues with the UART baud rate and the clock frequency, the problems were fixed with a few bodge wires and a new crystal oscillator. With those fixes, the 8080 was up and running, and able to be programmed via USB from a host computer.

On that topic, MarkTheQuasiEngineer plans to release another video soon, in which he details how the 8080 can be programmed. He also plans to do some benchmarking to show just how well (or rather, how slowly) this chip performs. Be sure to check back in for updates!