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

[Little John]

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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