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

[Little John]

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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