Restoration of a PDP-8a - test-drb@ccmp.vtda.org

15 Jan 2014

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 Message: 12
 Date: Tue, 14 Jan 2014 10:24:57 +0000
 From: anders at abc80.net
 To: "General Discussion\: On-Topic Posts Only" <cctech at
classiccmp.org>
 Subject: Re: Restoration of a PDP-8a
 Message-ID:
         <20140114102457.Horde.jcUVy0nXMOJSjET97Z2yBA7 at blue.abc80.net>
 Content-Type: text/plain; charset=UTF-8; format=flowed; DelSp=Yes

 Hi,

 Slowly my restoration project continues. I have repaired the power
 supply and I actually found and bought a programmers console. I also
 got a DKC8-A in etch revision D. I have now all the boards needed for
 getting this machine running.

 Is the two cables between KC8 and DKC8 just two strait 40 pin cables?

 I have a question about memory configuration. I have two core stacks
 from different suppliers. One from DEC and one from Dataram corp. The
 later one is impossible to find any information on. The DEC stack is a
 MM8-AB 16k module but the address field configuration looks strange.
 If I interpreted the manual correct it's configured as a 8k module
 using field 4-5.

 Picture of the jumpers on the actual board:
 http://www.abc80.net/docs/pdp8/pdp8a/DSC_2258.JPG

 Pictures on the complete board on both sides.
 http://www.abc80.net/docs/pdp8/pdp8a/DSC_2252.JPG
 http://www.abc80.net/docs/pdp8/pdp8a/DSC_2253.JPG

 The board is known good and does not origin from this particular machine.

 Does anybody know why this looks like this?

 /Anders

The PDP-8/A Operator's handbook at
http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp8/pdp8a/EK-8A001-OP…,
page 3-30 states that two BC08R cables are used.  The Digital Cables
Handbook at http://www.pdp8online.com/bklatt/cables.html describe the
BC08R on pages 30 & 31.  Page 31 shows the pinout.

About the Dataram module:  Does any of the info at
http://bitsavers.informatik.uni-stuttgart.de/pdf/dataram/ help?  Also,
there is a Dataram company (http://www.dataram.com/) still in business
providing computer memory products (since 1967).  Have you tried to
contact them?  You might get lucky, especially if they like the idea
of one of their "early" products still in operation after 30+ years.

The MM8-AA & MM8-AB Engineering Specification at
http://www.pdp8online.com/pdp8cgi/query_docs/tifftopdf.pl/pdp8prints/mm8aa.…
shows that your jumpers are in locations 1-3 & 3-4.  It then states
that those two jumpers, in combination, will configure the module for
memory locations 32K-48K, which it then states are "presently not
available."  But it was written in 1975.  However, the 1978 KT8-A
Memory Management Control (EK-KT08A-UG-001 at
http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp8/pdp8a/EK-KT08A-UG…)
allows an -8/A to use up to 128K of any -8/A memory type.  Perhaps the
previous user of the MM8-AB module had the KT8-A module to allow the
use of more than 32K?

Bob