[Coco] coco cartriges

[Arthur Flexser]

One way to find out if it is 4K or 8K would be to plug the cartridge in
after taping over the pins that cause the autostart, and check the contents
of memory at $C000 and $D000.  If the code at $D000 is a duplicate (ghost)
of that at $C000, then it's a 4K Rompack.  Which doesn't necessarily mean
it would be incompatible with an 8K EPROM, or difficult to make it
compatible by connecting the unused (possibly grounded or tied high)
address line to the relevant pin on the cartridge connector.  (On a CoCo 3,
you'd first need to do a POKE&HFFDE,0 to put it in ROM mode in order to see
the cartridge contents.)

A 24-pin EPROM that is compatible with that used in the CoCo's disk
controller is very difficult to find.  The 68764 and 68766 fill the bill,
but are almost unobtainable nowadays, though an adapter or hand-rewiring
can allow use of a compatible 28-pin EPROM like the 2764, which is much
easier to obtain.  You might be better off hunting for a cartridge that
already has a 28-pin ROM.

Art

On Tue, Oct 21, 2014 at 4:08 PM, didier derny <didier at aida.org> wrote:

> I got a  coco2 cartrige on ebay.
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> I opened it, without breaking it J
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> I found inside  a small board that can contains  2 x 24 pins roms
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> On my cartridge, there is only one rom installed..
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> Are these roms 4k or 8k ?  any eprom compatible with these eprom  ?
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> Marking on the eprom:
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> SCM90706P
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> TANDY  C 1981
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> 8070033
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> M 8140
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> Any way to use this cartridge to install a rom to start drivewire ?
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> Thanks
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> Didier
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> --
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