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

Computer Doc computerdoc at sc.rr.com
Thu Jun 28 05:50:19 EDT 2012

Hello Everybody,

Thank you all for the tips on places from which I can order the Motorola &
Hitachi chips.  I recently received NEW chips, both 68B09 and 63C09, from
UTSource.net!  I must admit I didn't ever expect to be able to order new
chips these days!  

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.  

The only task left, to complete my version of Grant's 6-chip 6809 computer,
is to program an EPROM with the 6809 Extended Basic.  I'm just waiting for
my UV EPROM Eraser to arrive so I can erase my 27C128 EPROM and program
Grant's 6809 Extended Basic into it.  I've already read it with Willem's
GQ-4X True USB EPROM Programmer that I connected to my Quad-core 8MB RAM
laptop PC running Windows 7 and it worked great reading the 27C128 EPROM!  I
still has an old Pheonix BIOS in it!  I'll then be able to test my first
home-built 6809 computer!  Yeh!  I can hardly wait!  

I'd like to experiment with a Western Digital 2793 or 2797 disk controller
chip design or maybe interface the SuperIDE cartridge to it so I can run
NitrOS-9 Level I.  Later, after adding a MM scheme,  I like to run NitrOS-9
Level II on this home-built 6809 computer.  If I can't find a simpler MM
scheme then COCO 3's version,  I might have to implement Coco 3's more
complex version of memory management.   If I used the SuperIDE CF & Floppy
disk Controller,  HDBDOS would have to be modified to use this 6809 Extended
Basic.  I wonder how involved that will be.  

Could NITROS-9 be changed to boot on this particular configuration?   All
communications is through the RS-232 port and no graphics will be supported.
Hum, HDBDOS with Drivewire 4 with some modifications would be very

I read somewhere on the internet that a different memory management scheme
had been created for the COCO 1 & 2 that had a driver written for OS-9 that
bank switched 32KB at a time, if memory serves.  If so, that would be easier
to implement then COCO 3's MM scheme.
I'm interested in using NitrOS-9 for 6809 assembly language and C language
development controlling various types of add-ons.   One I'd like to play
with is an AY-3-8910 Sound generator chip I just received a few days ago.
I'd like to update 6809 Extended Basic with some commands to control the
chip.  Does anyone have any 6809 code that could be used with the AY-3-8910
sound generator chip?

I'd also like to build a 6309 based system similar to Grand Searle's design
but using a monitor program written for the 6309 line of cpus.  Does anyone
know of such a monitor?  I could use a 6809 monitor, but I'd like to find
one written for the 6309.  Also any ideas for 6309 code are welcome.  I'd
like to think someone has written a monitor for the HD63C09 processor taking
advantage of its extended capabilities.  

I also received a  couple of MC68HC11A1P chips that I'm looking forward to
interfacing with.  I was very happy to find a monitor for the MC68HC11
processor on the internet.  

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


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