[Coco] rom swap with eprom?

[Steve C.]

In the morning light, I can now see the ghost of 12 cartridge pins that
have rubbed into either side of the 28-pin board through multiple uses. The
12v idea makes sense, didn't Tandy later remove that pin?

So I'd want to tie the extra address pins low, to make the cartridge match
the eprom burner's start location. (I hope.)

Many thanks for the pointers.

On Tue, Jan 12, 2016 at 12:17 AM, Dave Philipsen <dave at davebiz.com> wrote:

> I could understand deleting the 12v pin for that reason but there are 12
> pins missing on his cartridge.  I guess one could reason that you might as
> well leave off all unused pins just as a protection against any possibility
> of damage however slim.  Unfortunately for hacker types like me it meant
> that I couldn't use an old beat up cartridge pak just to experiment with to
> get at some of the other signals.  One thing that they got terribly wrong
> was not putting gold on the fingers.  That was a BIG mistake!
>
> Dave
>
>
>
> On 1/12/2016 1:48 AM, Arthur Flexser wrote:
>
>> 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
>>>>>
>>>>>
>>>>> --
>>> Coco mailing list
>>> Coco at maltedmedia.com
>>> https://pairlist5.pair.net/mailman/listinfo/coco
>>>
>>>
>
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