[Coco] rom swap with eprom?

[Arthur Flexser]

I always figured that omitting some pins on cartridge edge connectors was
for a reason other than RS saving some minuscule amount, though that is
also a possiblity.  I think it was to minimize the chance of damaging the
CoCo if someone unwisely inserted or removed a cartridge with the power
on.  This would be likely if the 12V line got shorted to an adjacent pin in
the course of a slightly askew insertion or removal.  I never checked if
the missing pins included the 12V one and the ones next to it, but I bet
that is the case.

(I once damaged my CoCo 1 in its early days by absent-mindedly inserting a
cartridge with power on, but it was a third party one that had no missing
pins.  Coincidence?  I think not.)

Art

On Tue, Jan 12, 2016 at 1:51 AM, Dave Philipsen <dave at davebiz.com> wrote:

> Does the cartridge have only 28 pins but there are positions for 40 pins?
> Seems like I recall that may have been the case.  I guess they were really
> skimping when they tried to save money by not putting all the pins on the
> edge connector!
>
> I would guess that the ROM you found inside is a house numbered part that
> is a mask ROM with pretty much the same pinout as a 68764/6.  I also think
> the generic name for such a mask ROM was 2364.  Check out
> Retro-Innovations' adapter here: http://store.go4retro.com/2364-adapter/
> Just use the adapter and then you can use the much more available 2764
> EPROM instead.
>
> Dave
>
>
>
>
>
> On 1/12/2016 12:31 AM, Steve C. wrote:
>
>> Thanks for that, it will be helpful. My main source of confusion at this
>> point is the coco service manual, which has a layout of 40 cartridge
>> signals, with a schematic on the next page showing 36 pins on the
>> cartridge
>> port. The cart itself has only 28 pins! I think I will concentrate on the
>> chip end of the thing as per your reference link and ignore the edge
>> connector confusion if at all possible.
>>
>> On Mon, Jan 11, 2016 at 10:24 PM, Barry Nelson <
>> barry.nelson at amobiledevice.com> wrote:
>>
>> Try this information:
>>>
>>> http://ist.uwaterloo.ca/~schepers/sockets.html
>>>
>>> Even though this is for a Commodore computer, I have found the ROM
>>> pinouts
>>> to be the same.
>>>
>>> Steve C. towmater at gmail.com
>>>> Tue Jan 12 00:58:13 EST 2016
>>>>
>>>> I bought a "Personal Finance" cartridge with the intention of swapping
>>>>
>>> the
>>>
>>>> rom chip inside with a Drivewire eprom, but upon opening the  cart I've
>>>> found a 24-pin un-google-able motorola part number ca 1980. I will spend
>>>> the hours searching for a schema on the web, but if anyone has a
>>>> shortcut
>>>> to knowledge about compatibility with 27xxx eproms with the shack's
>>>>
>>> chips,
>>>
>>>> please chime in and save me some eyestrain!
>>>>
>>>> -Steve
>>>>
>>>
>>> --
>>> Coco mailing list
>>> Coco at maltedmedia.com
>>> https://pairlist5.pair.net/mailman/listinfo/coco
>>>
>>>
>
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