[Coco] Memory Expansion Beyond 64k for the Coco 2

Bruce W. Calkins brucewcalkins at charter.net
Thu Jun 28 09:04:49 EDT 2012

There was the J&R Banker which used piggy-backed 64k chips for 128k or 256k 
chips for their 256k versions.  Use of the extra memory was clumsy at best. 
The 6809 is a 64k CPU and unless the base computer design and the OS 
includes Memory Management the use of the additional memory is suited for 
little more than simple storage.  Attempting to run separate programs in the 
extra banks often resulted in crashes if the stack was not saved and 
recovered in the switch between banks.

FWIW; no one has yet published a patch allowing NitrOS9 to boot on the J&R 
Banker.  A patch included with the J&R Banker is needed to run OS-9 and all 
indications are something similar is needed for NitrOS9.

Bruce W.


----- Original Message ----- 

From: "Computer Doc"

> Hello Everybody,
> Is there a memory expansion upgrade available for the 64KB Coco 2?  I want
> to upgrade my 64KB Coco 2, and also add Memory Management (MM) of some 
> type
> to Grant Searle's 6-Chip 6809 Computer.  I say for the Coco 2 because it
> doesn't use a GIME chip, which except for the graphics portion and the
> MC68B21 PIA chips, it's close (not exactly of course) to Grant Searle's
> 6-chip 6809 computer which is also a 64KB design using 32KB of RAM and 
> 32KB
> of EPROM.  I've thought about bank switching 32KB of RAM at a time for a
> total of two banks.  I've drawn up some circuits with this design idea 
> using
> a 4Mb chip yielding 512KB of RAM, but I'll need to write a driver for
> NitrOS-9  eventually.

> That's all for now.  Happy '09ing! :-)
> Kip

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