Gratuitous use of another chip just for 2 OR gates to implement a 4:2 encoder. It's all less efficient and less practical than the dial-a-rom, in that the dar holds 16 roms and doesn't need another ic, and the dar programming connection is even simpler and more robust.
But it just amused me to have a direct selector without manually binary encoding dip switches because why not? And I didn't want it to require a tool to use either like a screwdriver. And of course I always want an open source option, and I'm not up to the task of coming up with an open source rex-alike but using a Lattice part and the open source toolchain. It's unfortunate timing but I had already started this at least 3 years ago but just never finished it. A non-working version has been sitting in that github since 2019. A few weeks ago I finally dusted it off and corrected my bonehead pinout error, dialled-in the programming connection so it works well (the holes are slightly closer together than the pins, and the pattern and amount of offset took some trial & error) and replaced dip switches with the slide switch & or gates. I had no idea the dar was in the works. Not that it would have stopped me, but I just mean to say this isn't a reaction. It's no competition anyway because only a very few people ever build these diy-only things. I want them to exist so the option is there, but almost no one actually employs it. So this is not touching anyone's sales. Besides, *16* roms. And of course really it's even sillier when rex exists which doesn't even need a programmer or adapter to load it's, what, 30? slots? But for other platforms 4 is plenty. There's only 2 roms total for the 600 for example. Still leaves 2 free slots for hacking. I just added the browser-friendly render of the schematic to the readme so you can see the bank-select. -- bkw On Sat, Feb 25, 2023, 8:18 PM Mike Stein <[email protected]> wrote: > How do you select among the 4 images? > > On Sat, Feb 25, 2023 at 6:50 PM Brian K. White <[email protected]> > wrote: > >> On 2/25/23 10:31, [email protected] wrote: >> > Morning all, >> > >> > I just made this video live this AM. The DARs for the Model T computers >> > have sold out already but my friend is making more. >> > >> > In this video we take a look at the ‘Dial-A-ROM’ a spiffy new multi-ROM >> > for vintage portable computers. It was designed by the same guy who did >> > the Backpack drive. First, we’ll learn how to use the Dial-A-ROM with >> > the ROM images that come preinstalled on it. Then we’ll see how to add >> > our own ROM images if we so desire. >> > >> > *https://youtu.be/CejyLsI0HIw <https://youtu.be/CejyLsI0HIw> >> > >> > Jeff Birt (Hey Birt!)* >> > >> >> And for the diy-er, I finally vetted these last week: >> https://github.com/bkw777/Teeprom/blob/master/4ROM.md >> >> -- >> bkw >> >>
