[Coladam] eBay auction

Rich Drushel drushel at apk.net
Sat Jun 13 22:34:19 CEST 2009


On Fri, June 12, 2009 8:26 pm, Frances and/or Richard Clee wrote:

> Meanwhile, the series of disassembled, closeup pictures is posted so
> perhaps Rich or geoff or Dale or someone can figure out what the damn
> things are, and if the better interests of the Adam community suggest we
> pursue them.
>
> So will those who know please speak up?

     Okay, now that my brain is clear (turns out I was in the onset
stages of a migraine when I was writing last time, eventually my vision
almost went out and my head was exploding for a few hours, ask Rin how
much sense I was making at the time), and I have had a chance to examine
the disassembly photos, here is what I think:

(1)  The most informative photo is the one with the diagonal color ribbon
cable, since that exposes much more of the underlying circuit board.  I
will refer to this photo in subsequent points.

(2)  The large 40-pin ceramic DIP marked "TAPE SIM", with its associated
chips (TTL logic 74LS273 and 74LS00, 2 static RAMs 2114) and metal oscillator
crystal, is clearly is 60701 microcontroller (EEPROM version of the 6801),
suggesting that the board is an ADAMnet device.  Somewhere around should also
be an LM339 quad comparator, a 14-pin DIP, which was always part of the ADAMnet
interface.  Possibly it is under the multicolor ribbon cables.  If it is absent,
then whatever the board originally did, it cannot in its present state be a
functional ADAMnet device, because the LM339 sits between the ADAMnet bus and
the 68701 -- it would never get any ADAMnet inputs.

(3)  The circuitry in the vicinity of the added DB-37 connector, especially
the blue rectangular trimpot (i.e., high-precision variable resistor with
a tiny adjustment screw sticking out horizontally), suggests to me that
maybe the original board was a prototype for a disk or tape drive.  I have
looked at the extant schematics

     http://drushel.cwru.edu/schematics/

but don't see any immediate matches to the chips whose names I can
read in the disassembly photos.

(4)  I count 19 wires in the top ribbon cable and 15 in the bottom cable
(composite of both disassembly photos).  That would leave 3 unused pins
on the DB-37 connector.  Very likely the signals are 16 address lines,
8 data lines, 2 ADAMnet lines (data and reset), and presumably other Z80
control signals of interest that get run out the sideport connector.

(5)  The circuit board appears to have been designed to fit into the
Expansion Module #1 case, even though the board is clearly *NOT* a
reworked Expansion Module #1 board.

**** WILD GUESS ****

     The circuit board was originally for prototype tape drives,
either as a prototype of the (apparently planned, since there are
ADAMnet device numbers reserved for them) tape 3/4 expansion unit,
or else for original development of tape drives in general.  Given
how fragile the existing connectors are for the tape drives (plus
the pain of installing them in the first place), I can imagine a
sideport-based unit being easier to plug/unplug during development
cycles.  The "TAPE SIM" 68701 just runs a dummy tape drive device
(or devices).  At the ADAMnet level, all the user cares about is
reading and writing data, and if the 68701 does what is expected,
then it doesn't matter that there is no real tape drive attached.

***** END WILD GUESS *****

     I personally would like to have one of these devices.  But
as stated before, I have never used eBay, so I am the wrong person
to ask about bidding.  But I am willing to contribute $$$ to someone
who knows how to win eBay auctions :-S

     *Rich*

-- 
Richard F. Drushel, Ph.D.            | "They fell:  for Heaven to them no hope
Department of Biology                |  imparts / Who hear not for the beating
Case Western Reserve University      |  of their hearts."
Cleveland, Ohio  44106-7080  U.S.A.  |         -- Edgar Allan Poe, "Al-Aaraaf"




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