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Newsgroups: comp.sys.nsc.32k
Subject: Re:  PC532 Expansion & other questions
Message-ID: <9011301817.AA18181@manatee.UUCP>
Date: 30 Nov 90 23:17:05 GMT
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I believe I screwed up the address the first time I posted this, so I
will give it another whirl..
 
> My board arrived.  Currently I'm pouring over the schematics before turning
> on the soldering iron.  I've got a couple of questions someone might be able
> to help me with.
> 
> 1) I note that the DUARTs live at ports 2800020, ...40, ...60, etc.  Yet the
>    address lines going into the 74138 imply that they should be at base
>    addresses ...10, ...20, ...30, etc.  Is the documentation correct?  If so,
>    is this an artifact of the decoding for the ICU?
> 
> 2) I'm interested in a little off-board expansion without going through the
>    SCSI bus (I'm not ready to tackle the design of a smart SCSI controller).
>    I was thinking of popping off one of the DUARTs, running a couple of addit-
>    ional address lines (and unused decoding lines from the '138)
>    over to the socket and building a daughterboard to plug into
>    the DUART socket.  I'd like to put a couple of parallel ports
>    (perhaps a 6522 or 8255), an 8530 (I want to build an Appletalk
>    interface), and some other devices.  Any problems anyone can warn
>    me about?
 
A couple of suggestions.  For the DUART positions, fabricate (with
breakable strip sockets) PGA style sockets.  Then mount the DUARTS
in the regular PLCC socket and plug this assembly into the PGA 
style socket.  The PGA style socket will provide the interconnect
flexibility you will require for expansion.

Also, note that PLCC sockets generally have slots on two diagonal
corners for chip extraction.  The slot width just so happens to be
the same width as the thickness of a typical PC board -- thus
making it possible to attach a prototype board to the PLCC socket.
That is, the board is vertial to the socket and orientated along
the diagonal.  Wires then can be run from the socket to the proto-
type board, etc..  The end result is presto -- a pluggable assembly,
with lines [BD0..BD8], [A0..A3], /RD, /WR, /CS, /INT, etc. 
Also removing the associated RS232 drivers provides 2 * 6 (ie 12)
additional uncommitted lines to the assembly.

I trust the above is clear :-) -- just don't ask me to draw a picture
of it.

-- 
John Connin: manatee Orlando, Florida
         UUCP: {uunet,ge-dab,ucf-cs}!tarpit!tous!manatee!johnc