Some folks become involved in retro computing to relive the expertise of taking part in a favourite online game from childhood, whereas others wish to spend their time repairing the {hardware} or hacking away at new software program to show these outdated canines new tips. Whichever approach you occur to go, you will discover that you just ultimately want to switch (or reprogram) a ROM chip. These early reminiscence chips saved every part from working methods and programming languages to functions and character set definitions.
Usually talking, the ROM chips that had been present in traditional methods from the Nineteen Seventies and Eighties are nonetheless obtainable for buy immediately, and at low costs, so they don’t seem to be precisely onerous to come back by. However they could be a problem to work with, particularly if you wish to iterate on new designs quickly. The chip needs to be pulled from the machine, then its contents must be overwritten with a ROM programmer. The chips could also be new, however the workflow continues to be fairly dated.
SDRR (left) and the ROM chip it replaces (📷: piers rocks)
So for people who need a extra fashionable growth course of, Piers Finlayson has provide you with a fantastic answer. Finlayson has developed what is known as the Software program Outlined Retro ROM (SDRR). It makes use of an STM32 microcontroller to simulate the operate of a ROM chip, which signifies that it may be programmed in additional fashionable methods, and with out having to tug the chip out of the {hardware}. Regardless of being primarily based on a very completely different know-how, SDRR was designed to fit into the identical actual footprints of actual ROM chips.
The open supply design of the {hardware} can work with a spread of STM32 microcontrollers, ranging in pace from 100 MHz to 180 MHz. That’s sufficient pace to emulate ROM chips in Commodore 64s, VIC-20s, and PETs, for starters — and towards the quicker finish of the spectrum, even some later machines. The firmware of SDRR helps emulation of 2364, 2332, and 2316 ROM chips, and there may be sufficient reminiscence to retailer as much as 16 completely different photos, which may be chosen by way of jumpers.
When you would reasonably not load a number of photos, you’ll be able to merely depart the machine related to the programmer whereas it’s in use. This makes it doable to replace the ROM contents in real-time, with out eradicating it from the {hardware}. Talking of the programmer, nothing particular or costly is required. Connecting a couple of wires to a Raspberry Pi Pico is all it takes (should you would reasonably use the Pico because the ROM emulator itself, try my PicoROM challenge).
Finlayson has put collectively some glorious documentation on the board that explains the way to create the {hardware}, program it, and use it in a retro pc. Remember to test it out in case you have acquired a hankering to do some retro pc hacking.
