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

[Little John]

Okay - I thought that was what Darren A was saying but wasn't sure.
----- Original Message ----- 
From: "Arthur Flexser" <flexser at fiu.edu>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Wednesday, October 13, 2010 1:15 AM
Subject: Re: [Coco] Need a FD 502 controller that can accept 28 pin roms


> That modification is only necessary because Extended ADOS-3 requires 16K 
> of
> EPROM space;  for an 8K DOS, the FD502 works fine as is, even if the DOS 
> is
> in a 27128 or 27512, so long as the code is in the correct 8K of the chip.
> The relevant address line is grounded on the FD502, and the modification
> requires cutting a trace to un-ground it along with running a jumper wire 
> to
> the edge connector.
>
> Art
> On Wed, Oct 13, 2010 at 2:03 AM, Little John <sales at gimechip.com> wrote:
>
>> Cool. I was going by what I had read in the Extended ADOS-3 Manual which
>> states:
>> If you have the Tandy FD-502 controller, you already have a 28-pin 
>> socket:
>> however, the controller needs a minor modification in order to be usable
>> with a 27128 EPROM.
>> It then mentions how to get the instructions from SpectroSystems, 
>> followed
>> by:
>> The instructions may also be found on Page 76 of the March 1989 Rainbow
>> magazine except that there is a typographical error: It is pin 26 not pin 
>> 28
>> that must be connected to the controller's edge connector.
>>
>> But are you saying it can handle a 16K EPROM without modifications? or 
>> are
>> you saying that it can use any 2764-27512, but only as an 8K device? Just
>> curious. I use 27256's for everything because I have a ton of them - I 
>> just
>> burn an 8K image into the 27256 stacked 4 times - so it doesn't matter 
>> the
>> status of the upper address lines or even if they are floating - it still
>> works.
>>
>> If HDB-DOS is only 8K then it would be fine without mods, but if you 
>> tried
>> a 16K DOS (like CoCoNet) it would need the mod - I think?
>> -John #1
>>
>>
>> ----- Original Message ----- From: "Darren A" <mechacoco at gmail.com>
>> To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
>> Sent: Wednesday, October 13, 2010 12:24 AM
>> Subject: Re: [Coco] Need a FD 502 controller that can accept 28 pin roms
>>
>>
>> On 10/12/10, Little John wrote:
>>>
>>>> The FD-501 drives will work with the FD-502 controller (or pretty much
>>>> any
>>>> coco controller). I may be mistaken, but I believe that the FD-502,
>>>> although
>>>> having a 28-pin socket, is still only wired for an 8K eprom and the
>>>> additional address line will still need to be hacked into the socket 
>>>> with
>>>> a
>>>> jumper wire. Can anyone else confirm this?
>>>>
>>>
>>> The FD-502 will accept anything from a 2764 to 27512 without
>>> modification.  For anything larger than a 2764, the code must be
>>> programmed into the upper-most 8K of the device.
>>>
>>> Darren
>>>
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>>
>>
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