Subject: PDP-8A and Dual floppies

From: [email-masked] (Huw Davies)
Date: Wed, 5 Jan 1994 08:34:14 GMT

I'm trying to get a PDP-8A going as part of a demonstration for an
upcoming DECUS event. The problem is that I have a wide ribbon cable
that runs from the floppy controller and I had assumed that it would
just plug into the 8" drives. The problem is my usual one - sex! Both the
end of the cable and the socket in the drive are of the same (male) sex.
Should I just create a female-female cable and plug it in, or is there
some other magic required?
-- 
  Huw Davies           | [email-masked]
  Computing Services   | Phone: +61 3 479 1500   Fax: +61 3 479 1999
  La Trobe University  | I own an Alfa to keep me poor in a monetary
  Melbourne Australia  | sense, but rich in so many other ways

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From: [email-masked] (Ethan Dicks)
Date: 5 Jan 1994 13:40:18 -0500

In article <[email-masked]>,
>some other magic required?

No magic.  The standard cable has two 40-pin IDC connectors on each end
of a 40-wire ribbon cable.  It's one of the most ordinary cables used in
DEC hardware.  If you have to make one, just crimp a 40-pin connector
on each end of the cable.  I've got a bin of them, but shipping precludes
an easy solution.  Perhaps someone in OZ could help you out.

Others can probably quote the DEC part number (BC???-??) from memory, I cannot.
My best guess is BC08R-10 (for a 10' (3m) cable), but it could be a BC06R-10.

If you have a ribbon cable already coming out of the controller, what is on
the end of it that won't fit into the respective connector on the RX02?

-ethan
-- 
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From: [email-masked] (Charles Lasner)
Date: 5 Jan 1994 19:55:30 GMT

In article <[email-masked]>,

>of a 40-wire ribbon cable.  It's one of the most ordinary cables used in

I think I see a major problem here: Is Huw trying to hook a *drive* to an
RX8E or an RX01/02?

The RX01/02 is not merely a floppy drive.  Rather it's a complete
sub-system which you communicate with via a fast serial interface with
commands and data, not floppy signals at all.  In turn, the drives within
the RX01/02 aren't industry standard because more of the drive electronics
are found on boards within the box than in the drive whereas industry
practice is to place the read/write electonics within the drive itself. 
Indeed, the earliest RX01 drives were Calcomp CDS-140 drives with the
electronics removed!  All that remains is the motor and head assemblies.

The standard cable for the RX controller <-> RX subsystem is generally a
40-pin flat ribbon cable coming out of the drive.  The simplest connection
is directly to the RX8E via a flat 40-pin male-male cable called BC05-L. 
The reason this isn't one of the BC06 or 08 family has to do with
notation:  DEC's "normal" convention is to number cables that are 40-pin
as pin A-VV on one end and VV-A on the other, i.e., there is a wire
connection from pin A to pin VV on the far end.  There are also cables
that label A-A and VV-VV for conventional interconnections, etc.  (These
would be BC08R and BC08S respectively.) But the problem is that these
cables are labeled "This side up" in a way consistent with the wiring
convention; the engineer assigned to the RX project didn't understand this
convention, and created what is essentially a cable that is the same as
BC08S but you have to *not* lay the cable down backwards as is normal,
thus this particular cable has to have a label on the "wrong" side, thus
the alternate part number. 

Thus, all of these cables are just 40-pin flat ribbon cables; you just
have to determine how to properly plug in the ends!  (Note: the BC06
cables are shielded variants however!  This also applies to some of the
BC08 family as well, such as the positive bus and data break cables for
the KD8E and KA8E; DEC has had several generations of shielded cables with
different characteristics; I suspect the specific details of the
differences are overstated and are actually interchageable in most
applications.  However, I would hesitate to use an unshielded cable where
a shielded one was specified!)  Since the RX controller drives the cable
well, unshielded cable is normal for this application.

In some other applications, the cabling is a bit more complicated.  Some
controllers output the controller signals on 40-pin connectors, but the
cable has a DB-25 on the other end.  This is because a standard option of
the table-top version of the RX drive is a bulk-head mounted DB-25 mating
connector that in turn has an internal 40-pin cable that plugs into the
drive board, etc.  Thus, external cabling is via a shielded variant of
RS-232 cable!

In the pedestal versions, 40-pin ribbon cable is used internally.  The end
farthest from the drive electronics connects to a bulkhead connector with
ferroid RFI chokes on each data lead and a DB-25 connector.  On a DECmate
I or DECmate II with RX78, a DB-37 <-> DB25 cable is used to connect the
computer to the drives.  I have the rare dual pedestal pair version that
has two internal cables to the bulkhead connector with DB-37 (which is
compatible with VT-78, VT-278 and RX-78, all of which support two pairs of
drives).

cjl

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From: [email-masked] (Huw Davies)
Date: Thu, 6 Jan 1994 10:12:26 GMT

>an easy solution.  Perhaps someone in OZ could help you out.

Constructing the cable wasn't difficult, it was just that I didn't want
to destroy the one and only -8A that I have access to. Normally in
self-maintenance mode I check with another identical system before
making any cables/changes etc (this works really well with our 11/785s
and 8800s under my maintenance care).

>the end of it that won't fit into the respective connector on the RX02?

A simple male connector at both the CPU and RX01 ends.

The good news is that the -8A booted for the first time earlier today.
I've even run a couple of basic programs (Snoopy amongst them) which
brought back some memories. Tomorrow I've promised myself to read a
little more about OS/8 and see if I can compile a simple FORTRAN
program.

On a related issue, where can I get a copy of FOCAL for the -8 and how
do I get it onto the machine?

There is a possibility that later this month that the -8A and an 11/44
that I'm setting up will appear on the net. Stay tuned for details...

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From: [email-masked] (Paul Repacholi)
Date: 8 Jan 94 04:12:53 +0900

> that I'm setting up will appear on the net. Stay tuned for details...

I think I've got a copy of Focal-8 on... paper tape. I'll have a look tomorrow,
( Sat, when I wake up. ) I think this is when I get to fix my paper
tape reader. We could also check UWA education, they had an 8 they did
data loging with.

~Paul