[Coco] make-do ROM Paks

[Roger Taylor]

At 11:32 AM 9/16/2007, you wrote:
>>From: Roger Taylor
>>Subject: [Coco] J & M Systems floppy controller
>>Date: Sat, 15 Sep 2007 22:48:29 -0500
>>
>>
>>I doubt I will ever use this as a controller so it looks like a 
>>good candidate for a "ROM Pak" project board, if I can peel away 
>>any unneeded edge pins/fingers and just leave the ROM-required ones.
>>
>>It's a 24-pin ROM socket so obviously it can't use a 28-pin 2764 
>>(8k) EPROM, but it should be able to use a 2732 (4K) EPROM, 
>>correct?  I'm just not sure why a 24-pin 8K ROM wouldn't be pin for 
>>pin compatible with some EPROM of the same capacity.  Didn't 
>>someone mention such an EPROM recently?
>-
>
>Roger,
>
>The 24-pin sockets in CoCo controllers are not wired to accept a 
>2732. In particular, pins 18 and 21 have different signals:
>
>2732:
>pin 18  -  Chip Enable (active low)
>pin 21  -  A11
>
>Controller Socket:
>pin 18  -  A11
>pin 21  -  A12
>
>The 68766 (or 68764) EPROMS are directly compatible with the 24 pin 
>sockets in CoCo controllers, but can be hard to find these days. You 
>could also get a 'DOS Adpater' from Cloud 9 which allows you to use 
>the easier to obtain 2764 or 27128.



Hopefully there is a direct replacement (pins and voltage) for the 
24-pin ROM types that are used in our old CoCo game paks.  The board 
design is what I'm wanting to use, with a 24-pin socket, and some 
kind of 24-pin 8K EPROM that doesn't require 25 volts to operate or 
program.  The idea is to clone a CoCo ROM Pak board, socket it, 
insert an 8K EPROM, *but*.... at this point the way things are 
looking, a 4K EPROM will probably do just fine.

I can code pretty tight and can do serious things in 4K.  If a 2732 
won't work in an old socketed ROM Pak, then I'll probably need to get 
a mess of boards made for the common 2764.  I'm not seeking a ROM 
adapter for this kind of project, and I'm aware of Cloud-9's great product.



-- 
Roger Taylor