[Coco] Need a FD 502 controller that can accept 28 pin roms

[Arthur Flexser]

Actually, I don't think that putting in a 32K ROM in the disk controller
would have allowed access to the whole thing (except by using a mechanical
switcher).
The address space only allows for a 16K external ROM, I believe ($C000 to
$FFFF).  Maybe I'm missing something, but I don't believe you'd be able to
access the other 16K through software.  Not enough address lines.  (There
may have been game Rompacks with more than 16K, but they had some additional
hardware for bank switching.)

Art
On Wed, Oct 13, 2010 at 12:15 PM, Little John <sales at gimechip.com> wrote:

> Yes,
> the CoCo 3 could have accessed almost the entire 32K of ROM - it would have
> allowed some cool stuff.
>
> ----- Original Message ----- From: "Arthur Flexser" <flexser at fiu.edu>
>
> To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
> Sent: Wednesday, October 13, 2010 1:45 AM
> Subject: Re: [Coco] Need a FD 502 controller that can accept 28 pin roms
>
>
>
> Ah!  I had misremembered that the pin was grounded rather than tied high on
>> the FD502, and was therefore puzzled as to why the code had to be in the
>> UPPERmost 8K.  Thanks for the correction!
>>
>> This brings to mind an exchange I had at a Rainbowfest with Tandy's Mark
>> Siegel, who was the main guy involved with CoCo development (and the
>> keynote
>> speaker at that fest).  I mentioned how easy it would have been to enable
>> the full address space on the FD502 rather than tying that line high or
>> low,
>> and expressed the wish that any subsequent CoCo controllers have that
>> feature.  He agreed suspiciously quickly to implement this change on
>> future
>> CoCo controllers.
>>
>> Art
>>
>> On Wed, Oct 13, 2010 at 2:29 AM, Darren A <mechacoco at gmail.com> wrote:
>>
>> On 10/13/10, Little John <sales at gimechip.com> wrote:
>>> > Okay - I thought that was what Darren A was saying but wasn't sure.
>>>
>>>
>>> Yes. The FD-502 ROM socket is only wired for 8K (A0-A12).  You need to
>>> run a jumper wire for A13 if you want to use a 16K EPROM.
>>>
>>> The other pins which become address lines on larger EPROMS are all
>>> tied to Vcc, thus the need to put the code in the upper-most 8K of the
>>> device.
>>>
>>> Darren
>>>
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>>>
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