A favourite pastime of retro computing and pc engineering hobbyists entails getting classic CPUs up and operating from scratch. Whether or not it’s a 6502, Z80, or an early Intel chip, this is a wonderful approach to be taught extra about how computer systems work whereas having some enjoyable within the course of. Step one is often a free-run on a breadboard, wherein the CPU is regularly fed a NOP instruction in order that it perpetually cycles by means of its handle area sequentially.
That is sufficient to present that the processor is alive and kicking, and that you would be able to handle the facility and management indicators, however after watching the handle values rely up for a couple of minutes, it begins to get outdated. Naturally, the following step is to construct some sort of usable pc across the chip, however that could be a a lot greater effort, so the place do you get began?
An 8080 processor (📷: MarkTheQuasiEngineer)
There are any variety of methods one can go at that time, however YouTuber MarkTheQuasiEngineer lays out one possibility intimately. He wished to run a 50-year-old Intel 8080 CPU, and be capable of work together with it and program it from a contemporary pc. His answer concerned designing a customized system board that used all trendy {hardware} to interface with the 8080.
The construct has three major parts: an interface to a contemporary pc by way of a USB-to-UART chip, a simulated 8080 system full with RAM, management indicators, buses, and a clock sign, and eventually, the 8080 itself. To deal with the USB-to-UART operate, an STM32 microcontroller was chosen. Simulating the {hardware} of an 8080 system is a little more complicated, so a Microchip FPGA was utilized. That allowed MarkTheQuasiEngineer to construct all the mandatory parts into one chip.
Between the fashionable {hardware} and the 8080, a lot of completely different voltage ranges have been wanted. The USB-C connection solely provides 5 volts, however 1v2, 3v3, -5 and 12 volt rails have been additionally wanted. And that meant a lot of voltage stage shifters, that are a few of the most distinguished options on the customized PCB that MarkTheQuasiEngineer designed for the venture.
As soon as that shiny new PCB arrived, issues didn’t work as anticipated. Doesn’t it all the time appear to go that approach on the primary attempt? However thankfully, after debugging points with the UART baud charge and the clock frequency, the issues have been mounted with a number of bodge wires and a brand new crystal oscillator. With these fixes, the 8080 was up and operating, and capable of be programmed by way of USB from a bunch pc.
On that matter, MarkTheQuasiEngineer plans to launch one other video quickly, wherein he particulars how the 8080 could be programmed. He additionally plans to do some benchmarking to point out simply how nicely (or quite, how slowly) this chip performs. Make sure to verify again in for updates!
