PDP-8: (and others) anyone tried NVRAM simulation of hard drives? - test-drb@ccmp.vtda.org

2 Feb 2003

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   From: Ethan
Dicks &lt;erd_6502(a)yahoo.com&gt; 
That was one of my options.  Any ideas about what to use for the
cabling?
 If you are keeping it short ribbon cable should work fine.  If you were
running longer cables for multiple devices it might not be the best.

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 What would you estimate the entire harness to run? 
$100?
 I think you need 10 or 11 boards which the cheapest was about $7 so it could
be done for that.  The cable connection will be tricky on the cheap extender
card.  The grid card would be the best but most expensive.

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 I was thinking of recycling the COMBOARD design - 1/4
of the memory
map is "shared memory" - there is a circuit between the 68000 and
the host bus that initiates DMA cycles when the 68000 reads/writes
to it.  I have used a COMBOARD to test the RAM in a PDP-11/03 via
this shared memory interface.
 Don't know if the 68000 has a fast enough clock to see the pulses or it
will need a little hardware assist.  As long as you don't mind your peripheral
being brighter than the computer it should be viable.

From: Bob Shannon &lt;bshannon(a)tiac.net&gt;
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I beleive that Al got a few (one or two?) Augat wire-wrap quad DEC 
modules along with the CADR
hardware.  There was at least one quad unibus Chaos net interface board. 
But I have no idea of what an omnibus interface looks like electrically. 
 Is this a painful thing to build?
 Omnibus timing is a little strange but not that hard to work with.
It is similar to the 8/I external bus which is a daisy chained bus
with 10 or 11 cables for full version.