DEC stuff is so cool! They were sneaky and smart!

From: Jerome Fine <jhfine_at_idirect.com>
Date: Sun Oct 31 08:37:50 1999

>Tony Duell wrote:

> > anything like that in my 31 years of life! Remove the STP and what you
> > got? a standard WORKING Vt100? No soldering! No trace cutting? and I love
> > this! No DIP Switches to switch!
> > In fact I bet one could even replace that STP with a generic
> > computer such as the SB180! or perhaps the guts of a H89 (using the Vt100
> > as a console!
> You can. There's a thing called a VT103 (which I don't have :-(). It's a
> VT100 with a 4-slot Q-bus backplane inside (!). There's a paddleboard in
> the STP slot that links to 2 ports on a DLV11-J (4-port RS232) card in
> the backplane. The VT100 becomes the console for whatever processor you
> stick in the Q-bus, while the connector on the back is a normal serial
> port, also on the Q-bus system...

Jerome Fine replies:

I actually have a couple of VT103 systems. Only ONE has the STP paddleboard.
So if someone has a spare paddleboard, it would be appreciated - if you have a
VT103 that no longer works is about the only way that will happen.

In point of fact, while the paddleboard is convenient - actually extremely convenient -
it is not necessary. From what I understand, the paddleboard has the circuitry to
re-route the "console port" from the DLV11-J directly to the terminal without
going through the DB-25 in the back as a normal VT100 would require. PLUS,
the second channel in the paddle board then takes over the circuit to the DB-25
in the back which becomes an output port - usually to a printer, but it can be sent
to any other device as well including another terminal. What is VERY unique at that
point is that the SETUP selections which normally control the baud rate for the console
device are used instead for the DB-25 in the back (as they were designed to
control in the first place). If someone is interested in this explanation and did not
understand, please ask for clarification.

NOW, without the paddleboard, just use everything in the usual manner. The
backplane in the VT103 and the "console" device are now entirely separate.
Use the DLV11-J in the normal manner and connect the cable from the "console
port" on the DLV11-J to the DB-25 on the back of the VT103 (VT100 in a
wolf's costume).

One point which probably needs to be clarified is that when the paddle board
is in use, DO NOT connect the baud rate wire wrap pins for those channels
to the baud rate pins. The use of the paddleboard means that the baud rate
must "float". The console is automatically set to 9600 baud at that point and
the "secondary port" is set by the SETUP options on the VT103 itself.

If the paddleboard is not used, set the baud rate wire wrap pins in the normal
manner.

FINALLY, the 2 VT103 systems that I have are 22 bit backplanes. The extra
4 address lines have been soldered at each of the 8 required points. Thus, they are
able to (and on occasion just to test that it was possible) manage all 4 MBytes
of memory for a PDP-11 system. HOWEVER, (EXTREME????) WARNING!!
I have been told to never put a M8190 (KDJ11-Bx) board into this backplane.
Since the backplane is ABAB, NOT ABCD, the M8190 quad boards do not
feel comfortable and may be severely damaged. Can someone please comment
on this point?? The use of a dual M8192 11/73 is very acceptable, but some
sort of boot rom is then required - usually on a third party disk controller.

ALSO EXTREME WARNING!! The standard power supply for a VT103
is able to output ONLY 16 amps on the 5 volts and very little on the 12 volts.
That includes the video board and the AVO as well. I don't have the figures
handy - ask if you need them. However, with a third party MFM disk controller
which needs only 2 amps on the 5 volts plus an 11/23 (M8186), DLV11-J,
256 KBytes of memory, RXV12 (M8049) and even a DRV11 (5 boards
all together), there is still enough power left over to run an RD51 (ST412
from Seagate). That was placed under the tube with about minus 1/64"
(it had to be squeezed in very carefully) to spare. The incarnation I saw
running even had a switch on the front to transfer the power feed from
internal to external for long term running of the disk drive - evidently
the person who placed the hard drive under the tube wanted to be able
to run the hard drive from an external power supply - probably a PC
power supply so as not the overload the VT103 except for short demos
(or so I was told). There was also a set of cables out the back to allow
a second MFM drive to be attached to the controller to expand the hard
drive capacity. Needless to say, that system was much faster than using
a TU58 as the system device.

While I definitely agree that the VT103 was a very interesting piece of
hardware, what I do not understand is why it was not extended - unless
DEC was so loath to admit that it could not add a hard drive at that point
since an RQDX1 or RQDX2 (both quad boards) required 6 amps on the
5 volts just for the controller plus another board for the boot ROMs and
that would have required a much better power supply. The VT103
appeared long before the RQDX3 was available.

What was very interesting when the VT103 was used for a demo
was that it could not be distinguished, at first glance, from a simple
VT100. So when the system was turned on and it started up running
an OS and all that by itself, it made quite an impression - especially
with the hard drive inside which was totally unexpected. This was
especially true if the usually unlabeled VT103 top plastic housing
was switched with a VT100. The only clue would be that the VT103
has a fan inside the space where the boards are kept whereas the
VT100 does not.

Sincerely yours,

Jerome Fine
Received on Sun Oct 31 1999 - 08:37:50 GMT