19 Jun
2005
19 Jun
'05
9:31 p.m.
Subject: Re: DSD-440 and/or drive recommendation for PDP-8
From: "vrs" <vrs at msn.com>
Date: Sun, 19 Jun 2005 21:19:21 -0700
To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>
Heres the trick. Don't copy the parts, copy the logic and use
standard TTL. Most all the functions are easily available or
or sometimes available in denser (newer relatively) parts.
Trying to copy verbatim will be hard unless you have a lot of
DEC junker cards to strip. However most of the logical functions
are simple so substitutions are not as scary.
Allison
Even if you don't have an RX8E its a trivial
board
easily copied.
I don't know about trivial (I am trying to do one). There are a lot of
unobtainium parts in an RX8E that have to be designed out of a modern clone.
(It's easily doable, but not trivial.) 
19 Jun
19 Jun
9:45 p.m.
From: "Allison" <ajp166 at bellatlantic.net>
From: "vrs" <vrs at msn.com>
Heh, I did that, but I shot myself in the foot by using the denser parts and
not quite getting it right.
Mine is actually a Posibus card (Ethan has the other prototype). There are
other problems with Omnibus cards, too. You can get the bus interface close
to spec., but not dead on, AFAIK with modern parts. Posibus is more
forgiving. (Though you can get close enough for small Omnibus backplanes
pretty easily.)
Vince
(It's easily doable, but not trivial.)
Heres the trick. Don't copy the parts, copy the logic and use
standard TTL. Most all the functions are easily available or
or sometimes available in denser (newer relatively) parts.
Trying to copy verbatim will be hard unless you have a lot of
DEC junker cards to strip. However most of the logical functions
are simple so substitutions are not as scary.
7127
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7127
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