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

[Arthur Flexser]

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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