[Coco] Proprietary, nonstandard memory expansion for the CoCo

Arthur Flexser flexser at fiu.edu
Fri Jun 8 22:00:43 EDT 2012

I have zero useful input to contribute on this, but just want to see
if my CoCo trivia neurons have come up with the correct tidbit on

Was the 256K CoCo 1/2 expansion you're describing called the "J&R
Banker" or something like that?


On Fri, Jun 8, 2012 at 3:31 PM, Juan Castro <jccyc1965 at gmail.com> wrote:
> This is a hack my (long-defunct) company did back in the day and I would
> eventually like to replicate it in a real CoCo someday.
> It's a 256 KB memory expansion for the CoCo... 1 or 2. Basically, you
> select, with a poke to some $FFxx, which of up to eight 32 KB banks will
> play the part of the "upper 32 KB" in a 64 KIB CoCo. (Which you then would
> select over the ROM in the usual way.) They raised one pin - SELECT pin? -
> of each of the "native" upper 32 KB memory chips out of the socket, wired
> them to one of the outputs of a 74LS138 and 6 of the other 7 ones to the
> extra 192 KB in the expansion*. It worked pretty well, and although it was
> compatible with precisely nothing, it was used in our in-house-developed
> business systems. Which did sell, believe it or not. Not really being an
> electronics person, I can't tell you what other chips were there, but would
> it be too difficult to concoct some schematic based on that description?
> Being a total newbie in OS-9, I wonder how easy it would be to make
> NitrOS-9 use that memory.
> Thoughts?
> * Yeah, that could theoretically make it a 288 KB memory expansion.
> Juan
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