If you have been building electronic hardware for several decades, do you still have any projects from your distant past? Do they work? An audio amplifier perhaps, or a bench power supply.
[Just4Fun] made a rather special computer in the 1980s, and it definitely still works. Describing it as “An 8085 single board computer with an EPROM emulator” though, does not convey just how special it is. This is not the modern sense of a single board computer with an SoC and a few support components. Instead it is a full system in the manner of the day in which processor, memory and peripherals are all separate components surrounded by 74 series glue logic. The whole system is wire-wrapped on a piece of perfboard and mounted very neatly in a rack. The EPROM emulator is a separate unit in a console case with hexadecimal keyboard and 7-segment display.
As the video below the break of an LED flashing demo shows, the EPROM emulator allows 8085 machine code to be entered byte by byte instead of having to be burned into a real EPROM.
[Just4Fun] leaves us with plans to replace the period EPROM emulator with a modern alternative, an EEPROM on a PCB designed to fit in the original bank of EPROM sockets. In this he suggests he might fit a bootloader and a BASIC interpreter, something entirely possible back in the day with conventional EPROMs, but probably not as cheaply.
If the 8085 has piqued your interest, you might like to read about the structure of its ALU, and its registers. if you’d like to try your hand at making an 8-bit computer of your own, we recently reviewed the RC2014, a Z80 machine.