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

[Little John]

There were some Tandy CoCo 3 Only 32K Rom Paks I think that used it, however 
some of them used Greg Zumwalts bank switching carts (which allowed all 
coco's to access more than 16K Rom Paks).

----- Original Message ----- 
From: "Arthur Flexser" <flexser at fiu.edu>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Wednesday, October 13, 2010 12:28 PM
Subject: Re: [Coco] Need a FD 502 controller that can accept 28 pin roms


> 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
>>>>>>
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>>>>>>
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