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

[Arthur Flexser]

Thanks, hadn't remembered that there was a 32K external ROM mode.  Anybody
know if there was ever a CoCo 3 product that made use of it??

Art

On Wed, Oct 13, 2010 at 1:09 PM, Little John <sales at gimechip.com> wrote:

> 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
>>>>>
>>>>> --
>>>>> Coco mailing list
>>>>> Coco at maltedmedia.com
>>>>> http://five.pairlist.net/mailman/listinfo/coco
>>>>>
>>>>>
>>>>> --
>>>> Coco mailing list
>>>> Coco at maltedmedia.com
>>>> http://five.pairlist.net/mailman/listinfo/coco
>>>>
>>>>
>>>
>>> --
>>> Coco mailing list
>>> Coco at maltedmedia.com
>>> http://five.pairlist.net/mailman/listinfo/coco
>>>
>>>
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> http://five.pairlist.net/mailman/listinfo/coco
>>
>
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco
>