[Coco] J & M Systems floppy controller

[Darren A.]

>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.

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