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

Arthur Flexser flexser at fiu.edu
Wed Oct 13 02:45:08 EDT 2010

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.


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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