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 technique 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, during which the CPU is regularly fed a NOP instruction in order that it perpetually cycles by means of its handle house sequentially.
That is sufficient to present that the processor is alive and kicking, and that you may handle the ability and management alerts, however after watching the handle values rely up for a couple of minutes, it begins to get outdated. Naturally, the subsequent step is to construct some kind of usable pc across the chip, however that may be a a lot larger 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 needed 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 resolution 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 through a USB-to-UART chip, a simulated 8080 system full with RAM, management alerts, 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, numerous completely different voltage ranges had been wanted. The USB-C connection solely provides 5 volts, however 1v2, 3v3, -5 and 12 volt rails had been additionally wanted. And that meant numerous voltage stage shifters, that are a few of the most outstanding options on the customized PCB that MarkTheQuasiEngineer designed for the undertaking.
As soon as that shiny new PCB arrived, issues didn’t work as anticipated. Doesn’t it at all times appear to go that method on the primary strive? However luckily, after debugging points with the UART baud charge and the clock frequency, the issues had been fastened with a number of bodge wires and a brand new crystal oscillator. With these fixes, the 8080 was up and operating, and in a position to be programmed through USB from a bunch pc.
On that subject, MarkTheQuasiEngineer plans to launch one other video quickly, during which he particulars how the 8080 could be programmed. He additionally plans to do some benchmarking to indicate simply how effectively (or moderately, how slowly) this chip performs. Make sure you verify again in for updates!
