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

[Little John]

The CoCo 3's GIME can be set to allow the CTS* to access a 32K external ROM.
The CoCo 1 and 2 can only access 16K

-John#1

----- Original Message ----- 
From: "Arthur Flexser" <flexser at fiu.edu>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Wednesday, October 13, 2010 11:56 AM
Subject: Re: [Coco] Need a FD 502 controller that can accept 28 pin roms


> 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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