Subject: Belated response to an old issue

From: [email-masked] (Charles Lasner)
Date: 13 Feb 1994 17:37:42 GMT

The following is an excerpt from an original post to pdp8-lovers in May, 
1989.

Date: 31-May-89 22:48:46 +0200
From: Johnny Billquist <[email-masked]>
To: [email-masked]
Subject: Expansion and memory...

I have a question for all you initiated omnibus eighters out there.

First of all. I have an 8/e, with an 8/a used as an expansion box.
I also have a paper, from dec, which tells a little about expansions
for the 8/e. The funny thing is, that this paper, specifies that
the backplane having the memory (the box with that backplane I mean)
ALWAYS should be on top. They make this extremely clear.

However, when I put together my current configuration, I hadn't read
this paper, and naturally (according to Murphy) I put the 8/e, with
all controllers on top, and the 8/a box, with memory below.
Now, this works just fins, never had any problems at all, so
why does (did) DEC think that one NEVER should do this?

	Just curious...
	Johnny

I don't have a definitive answer, but I can explain why JB's stated 
configuration goes against the configuration guide.

The designated way to connect the system he describes (incidentally, my 
current main system *is* as DEC describes) is to place the 8/e on the 
bottom and thus the 8/a on top.

The key mechanical reasons are that the following key cards are placed thus:

1)	KK8E cpu cards in front buss of 8/e box.

2)	Terminator in top slot of 8/a box.  This placement is considered 
mandatory; there's an ECO to the M8320 also mandatory which consists of 
*removing* a half-watt resistor.  The reason is that it's extraneous but 
harmless on the 8/e box but can be detrimental to the 8/a box.  It tends 
to "leak" DC between the full-power and standby-power legs for the 
purposes of preserving memory contents during short power outages (MOS 
memory in boxes with batteries) and will confuse the power-low/power-empty 
sequences, etc.

3)	The interconnect cable is always taken from the back of the 8/e 
box and is also always taken from the bottom of the 8/a box.

Note that there are several constraints within the 8/a box:

1)	All memory-related cards must be in the top slots because of KT8A 
considerations (fifth-foot).

2)	The option boards have to be in slots 2 and 3 (because of the 
power-low/power-empty wiring.

3)	The KK8F (8/e) CPU *must* be used.  With the terminators on the 
wrong end of the buss, the KK8A card cannot span more than one short-buss 
box, etc.  If the KK8E is in the 8/a box, it has to be at the bottom end 
because that's the only place to arrange the CPU with EAE.  Since there 
is an interconnect, the cable goes there instead with the CPU in the other 
box.

While not recommended in the guide as far as I can tell, I have seen 
in-house installations at DEC where they do it all "backwards", i.e., the 
CPU is in the bottom slots of the 8/a box, and then the interconnect 
cable runs from the top slot to the back of the 8/e box.  The terminator 
is in the next-to-front slot, just behind the 8/e front panel.  I have 
also seen in-house dual 8/e box systems done this same way.  I suspect 
it's all part of some "conventional wisdom" the field circus guys 
invented back when the KK8F was in need of lotsa long-buss oriented ECO's 
that came later.  (It's conceivable that when an early CPU was too flakey 
to run a particular system in two boxes, reversing the order this way 
changed buss reflections enough that the system did work a bit more 
reliably.  The guide was written long after these ECO's became standard.)

In any case, the original issue had to do with which box raises over 
which box.  Part of the answer lies with the interconnect cables:

When either 2 8/e boxes or 2 8/a boxes are inter-connected, the 
designated cabling is 2 pieces of BC08H cable, usually 4.5 feet long (-4f).

When the specific configuration is used, an obscure variation is used, 
the BC-80C cable.  This is a number that "fell through the cracks" and 
has always been extremely difficult to obtain, even when it was 
relatively new.  Part of the problem is that it made it's first 
appearance as part of the "FPP-8/e" which is the FPP-8/a cards packaged 
in a 12-slot box to be added onto the back of an 8/e box.

The BC-80C cable is a hex board with plated-through holes that 
"criss-cross" the buss connections.  Attached to the card are two white 
Omnibus cables that terminate the same way as a BC08H, etc.  Thus, the 
cable is designed to come out of the bottom of the 8/a box and have the 
white cables run underneath it in the crack between the bottom of the 8/a 
box and a *covered* 8/e box.  (Leaving off the 8/e box cover will destroy 
the cable; many of us are "guilty" of leaving the cover off on an 
8/e-only system!)  Thus, it's impossible to put the 8/a box beneath the 
8/e box.

I suspect that the configuration guide assumes the use of 8/a memory, 
thus the guidance is misguided :-).

I also suspect that JB didn't use the BC-80C cable, and instead attempted 
some "applied origamy" using a pair of BC08H cables to create a 
non-standard connection.  (Note: this is ugly, but functional!  Picture 
the problem of connecting an 8/a box to an 8/e box where the cards run 
the "wrong" way.  Folding the cables is unavoidable!)

While I do use a 20-slot box, my BC-80C cable was taken from an FPP-8/e.  
I was never able to acquire it as a part, nor even find it in any DEC 
parts guide (known to be notoriously inaccurate on all counts: part 
numbers, availability, and price).

(A digression to a "war story" on the DEC parts front:

DEC parts catalogs were merely printouts of LPT output reduced a little 
and printed on the cheap paper typically used for handbooks, etc.  
Clearly a computer-based database.

Certain parts were priced on a quantity 10 basis, but sometimes stated as 
a unit price which you then had to multiply by 10 to get your cost, since 
1 could not be purchased, etc.

When inconsistent methods are used to state cost, mistakes are bound to 
be made.  In the course of this, the blunder was made that made it appear 
that the DECtape drive guides were of grossly unequal price, i.e., the 
left guide cost about ten times the right guide!

I had to purchase replacement guides, and had to argue with a parts 
salesman over why it was a typo because in the previous catalog, each 
part was the same price, albeit both about 15% cheaper.  The guy was 
quite "inventive" and concocted an explanation:  He *knew* that DEC had 
switched vendors for left-hand guides, but not right-hand guides!

Many phone calls later, I eventually found someone who would listen to me
about the concept of a mistake in the database.  I was able to order them
at equal price, but he refused to have the database corrected.  (I suspect
they were under some form of "computers can do no wrong" policy.)

As the years went by, there were various managerial manipulations of 
parts price.  essentially, the older the part was, the more they jacked 
up the price to discourage you from maintaining the equipment.  I'll 
leave it to some business major to discuss justifying 100's of percent 
increase in general; DEC's business practices have gotten them to where 
they are today, etc.

In any case, because the two parts were never re-synced, they developed 
independent price-growth changes, apparently placed into separate price 
increase tiers, etc.

Curiously, this is partially self-correcting!  At some point, the right 
guide was "only" six times as expensive as in the last catalog before the 
incessant price rises while the left guide, elevated by a factor of ten 
already, had only doubled in cost!  Thus, instead of staying at a ratio 
of 10:1, the prices "converged" on being only 3.3:1.)

None of the parts people were ever able to identify the BC-80C.  Some of 
our readers have seen my machine; the part is quite real!

A question to a.s.p readers who are also on the pdp8-lovers list:

Is there a need to repeat items such as this, generated by past posts to 
pdp8-lovers, on the pdp8-lovers list, or is the propagation today 
sufficient via a.s.p?  I suspect that many of the original pdp8-lover's 
list people are a.s.p people today.  Please e-mail me if you have any 
ideas along these lines, etc.  In any case, I will continue to make 
"belated responses" where the topic warrants, etc.

cjl

ps: Does anyone have any expertise in setting up a listserver so that 
pdp-8 archive files at sunsite.unc.edu or elsewhere can be automatically 
mailed to the requestor?

---

From: [email-masked] (Johnny Billquist)
Date: 15 Feb 1994 12:54:06 GMT

>The following is an excerpt from an original post to pdp8-lovers in May, 

Wow. Long time ago. And I even remember it. (Yikes. :-)

>the "wrong" way.  Folding the cables is unavoidable!)

(Sorry about including all the message, but I didn't see any
good places for cutting, and not any good places before here
to insert my comments.)

Well, the system in question is in storage right now, so I can't
open it up. But I'll go on my memory for this one.

The CPU is right behind the 8/e panel.
The cables are unibus-cables, and connect at the back end of the
8/e, and the top of the 8/a.
I have two 16K core memories in the 8/a box.
The terminator (M8320) is in the bottom of the 8/a.
So, no twisted cables, no funny stuff at all, just things
placed very backwards to what DEC said.

>"belated responses" where the topic warrants, etc.

There are probably some people who might find it
interesting. I do at times. (But I have yet to see
you make a short answer to anything, cjl. :-)

>pdp-8 archive files at sunsite.unc.edu or elsewhere can be automatically 

Nope. But if someone have the software, I might be able to
set it up on a machine.
But why not just making it available for anonymous ftp.
There are ftpmail servers on many machines on the net, which
can then help those who only have mail access.

	Johnny

--
Johnny Billquist                  || "I'm on a bus
CS student at Uppsala University  ||  on a psychedelic trip
email: [email-masked]       ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

---

From: [email-masked] (Charles Lasner)
Date: 15 Feb 1994 23:10:38 GMT

In article <[email-masked]>,
>The CPU is right behind the 8/e panel.

That's the recommended configuration.

>8/e, and the top of the 8/a.

Nope.  Those are BC08H cables.  They superficially look like Unibus 
cables.  They are wired differently.  Actually, Unibus cables are weird; 
these BC08H cables are essentially straight-through wiring.

>I have two 16K core memories in the 8/a box.

Two MM8AB, same as me.

>The terminator (M8320) is in the bottom of the 8/a.

Consistent with this non-standard method.

>placed very backwards to what DEC said.

No, wrong.  Neglecting the fact that the 8/a has cards vertically stacked 
over each other and the 8/e has them stacked horizontally (the chassis 
essentially are 90 degreees out-of-phase with each other :-)) the cards 
in the 8/a box face backwards.  Berg connectors exit on the right in the 
8/a; the left in the 8/e.  In order to make that work (i have done it) 
you have to twist the two cables over each other, as I indicated.

The BC-80C does the "twisting" for you in its etch so the cables come out 
the way you would expect.

In any case, I agree with the electrical routine being "backwards" 
doesn't matter.  I explained my ideas that the configuration guide is 
mis-using its own reasoning to merely arbitrate what is actually just 
statistically likely.  But clearly, DEC's guidance rules are based on 
using the correct cabling.  Only the BC-80C applies here.  The BC08H pair 
is for use with a pair of like boxes only.

>you make a short answer to anything, cjl. :-)

That isn't the question!  I just want to know if the pdp8-lovers list has 
to be "cross-posted" in this regard.  Since the questions of this form 
are from that far back, is there a need to also post to the list, or is 
everyone from back then now reading alt.sys.pdp8?

In fact, can anyone provide some kind of net.statistics about who is on 
the mailing list *not* also on a.s.p?

>can then help those who only have mail access.

Anyone know what/how to do this?

cjl

---

From: [email-masked] (Stephen Quigg)
Date: Sun, 13 Feb 1994 21:50:34 GMT

In article <[email-masked]>,

>power-low/power-empty wiring.

  Also, the boot switch (switches if you have both panels), need the option
boards in slots 2, 3 to work.

---

From: [email-masked] (Charles Lasner)
Date: 17 Feb 1994 01:15:56 GMT

In article <[email-masked]>,
>boards in slots 2, 3 to work.

Yes.  The SW function of the boot switch is available on any buss slot, 
but the card has to initiate a power-ok-not sequence, etc.

To my knowledge, slots 2 and 3 are interchangeable?

cjl

---

From: [email-masked] (Johnny Billquist)
Date: 18 Feb 1994 16:17:39 GMT

>these BC08H cables are essentially straight-through wiring.

Sorry, but when I say they are Unibus-cables, they are Unibus-cables.
I grabbed them right out of a pdp-11.

>you have to twist the two cables over each other, as I indicated.

Hmmm, thinking of it, you're right, I must have them crossed
at least. But I don't remember twisting them.

>everyone from back then now reading alt.sys.pdp8?

The question wether people from back then are reading here
and now is hardly the most important question in this case.
I think it's more significant to ask; are the people here
today interested in those questions?
And my answer is; Yes, probably. There are people today who
also can benifit from getting more information, who wasn't
around at that time.
So, from this point of view, I think there is a good reason
for reposting those old questions.
Especially when they haven't been answered before.
If the subject had come to a good finish, you might let it
lie, and let people read the digests, though.

>the mailing list *not* also on a.s.p?

There is no way to find out who is reading news, so unfortunately
it's impossible to get such statistics.
Who's on the mailinglist can be found out, however.

>Anyone know what/how to do this?

Hmmm. Give me a day or so, and I'll look up where mailservers
are running. (If I don't forget this.)

	Johnny

---

From: [email-masked] (Charles Lasner)
Date: 19 Feb 1994 17:13:45 GMT

In article <[email-masked]>,

>I grabbed them right out of a pdp-11.

Go look at a unibus cable.  It shorts together several pins in the etch.  
The Omnibus doesn't have unused pins, especially on both halves.  Please 
explain how a shorted cable makes a passable Omnibus cable.

The BC08H cable is what the unibus cable should have been.  All pins are 
straight-through one-for-one.  Had DEC figured out how to do the jumpers 
for the Unibus granting, etc. on some separate jumper set on the end of 
the cable, we all would have used only one type of cable!  In essence, 
the BC08H is the "big brother" of the Omnibus jumper M935.  The only 
difference is the handles, the lack of mechanically joining the ends, and 
of course the length.  Note that the unibus has an analogy, the M920.

A curious aside: The M920 originally had a tape drawn around the base of 
it that often was imprinted "unibus" throughout.  (Some were plain like 
the bulk of the M935's.)  But I acquired a few M935's with the unibus 
tape on them :-).  Sometimes even DEC people can't tell the difference!

>at least. But I don't remember twisting them.

Crossing *is* twisting.  The left-most 8/e-box one comes out, does a 180 
degree twist and is placed into the 8/a box on the right, and vice-versa 
for the other cable.  Can't be helped due to the connectors facing the 
opposite way, etc.  (8/e component side towards front; 8/a components 
skyward.)

The BC-80C cable avoids this entirely because the cable joins onto the 
hex board without twists or crosses.  The lands on the card do a 
criss-cross on the module so that it all goes to the proper place 
anyway.  Thus, the cables come out and lie flat where you would want them 
to.  While I'm not too happy about running the cables under the 8/a box 
and above a covered 8/e box, I would be less happy attempting to run it 
above an 8/a box and under an 8/e box!  Thus, the 8/a box belongs *over* 
the 8/e box, which is where we came into this.  Electrically, I have no 
problem with it going in the top or bottom of the 8/a box though.  And of 
course if the boxes are separated in the rack it woudln't matter!

>lie, and let people read the digests, though.

If the issue is at rest, I have been skipping over them and merely 
archiving them.  If the issue is open, then I would think of posting to 
the list as well as a.s.p.  But I suspect that there may be a third kind 
only relevant to the "old gang" whom I suspect are largely now on a.s.p 
if not on both!

In any case, can anyone help us to "merge" the two things?  The ideal 
situation would  be a universal cross-posting regardless of source, etc.

>it's impossible to get such statistics.

Someone estimated that Alt.folklore.urban has 60,000 readers.  How does 
anyone create these statistics (other than out of thin air :-))?

>Who's on the mailinglist can be found out, however.

Can we get a posting to a.s.p of that list?  Then maybe we can get some 
responses from those who saw their names posted in a.s.p, etc.

>are running. (If I don't forget this.)

Hopefully, they can be made to carry a.s.p.

cjl

---

From: [email-masked] (Johnny Billquist)
Date: 20 Feb 1994 11:49:18 GMT

>explain how a shorted cable makes a passable Omnibus cable.

Beats me why it works, but it does. I haven't checked which lines
are shorted, and if they matter.
However, I certainly never even have had a reason to come close
to an Omnibus cable. All my pdp-8 systems have been in a single
box. The expansion was made from taking two systems and merging
them into one. And the cables definitely are Unibus cables.
Since this is getting to be a heated topic, I'll open up my
system next time I pass my parents, and make a through check
on it.

>opposite way, etc.  (8/e component side towards front; 8/a components 

I'll leave this until I've checked it again.

>situation would  be a universal cross-posting regardless of source, etc.

Hmmm. Someone who could set up a crossposting service between pdp8-lovers
and alt.sys.pdp8 then?
I might do that once I have a news-service running.
The thing has been done for info-pdp11 to vmsnet.pdp11, so I guess
I could get the help from those people there.

>anyone create these statistics (other than out of thin air :-))?

Make guesses from a small sample, tries to approximate the reach
of the newsgroup, and extrapolate a number.
In short: Just a little denser air.

>responses from those who saw their names posted in a.s.p, etc.

Just mail to [email-masked], asking for the list
should do it. If I remember right, Jan Brittenson is the one who
handles it. His email is [email-masked]. I don't think he has
passed it on, but primarily mail to the -request address.
Maybe they can set up a news-gate too.

>Hopefully, they can be made to carry a.s.p.

No, a mailserver can just access anonymous ftp-areas by mail.
However, it don't have to be their own ftp-area. That server
can access other ftp-areas as well.
(At least one ftpmail have been accessing our ftp-area, that
much I know...)

	Johnny