10 Aug
2019
10 Aug
'19
11:56 a.m.
The DEC VT20 terminal apparently included a PDP-11/05 with a direct mapped
character display and was intended for text editing and typesetting. It
seems to have been followed by the VT21, and then VT71/VT72, all three based
on an LSI-11 (KD11-F). There's a real lack of documentation about these
online, although the VT72 does have a print set.
Apparently the VT20 used the M792-YK as its bootstrap; the Field Guide is
silent regarding the boot device and M792 documentation stops earlier in the
series of variants.
According to the VT72 print set, it used the MRV11-VC (M9942-YC; described
in the Field Guide as a "bootstrap/diagnostic module") for its bootstrap but
is also silent regarding the boot device. In interestingly, the Field Guide
also describes a MRV11-AA (M7942-TB) as a "M7942 with VT52 emulator, VT71
bootstrap".
For async. communications the VT20 used a DL11-B (M7800 (EIA)). the VT72 a
DLV11-F (M8028).
Looking in a DEC "Options and Modules" listing I see VT20 bundles including
Typeset-11 and DECset-11, and it appears that the VT20 could be configured
with two displays & serial lines in a single 11/05.
So . is the boot device in these systems the remote host via the serial
line? What protocol would that have been? Something native to Typeset-11
and DECset-11?
paul
10 Aug
10 Aug
12:39 p.m.
On Aug 10, 2019, at 2:56 PM, Paul Birkel via cctech
<cctech at classiccmp.org> wrote:
The DEC VT20 terminal apparently included a PDP-11/05 with a direct mapped
character display and was intended for text editing and typesetting. It
seems to have been followed by the VT21, and then VT71/VT72, all three based
on an LSI-11 (KD11-F). There's a real lack of documentation about these
online, although the VT72 does have a print set.
...
Looking in a DEC "Options and Modules" listing I see VT20 bundles including
Typeset-11 and DECset-11, and it appears that the VT20 could be configured
with two displays & serial lines in a single 11/05.
So . is the boot device in these systems the remote host via the serial
line? What protocol would that have been? Something native to Typeset-11
and DECset-11?
I've never heard of DECset-11, but I worked on Typeset-11 1978-1980. The VT71 was the
standard high end terminal for that system. I saw a VT20 sitting in a corner of our lab,
but it was collecting dust and I never saw it operate, or connected to anything.
As far as I know, no trace of Typeset-11 or TMS-11 (same software pretty much, ported to a
stripped-down IAS instead of RSX-11/D) have been preserved.
It seems plausible that the download protocol would be DDCMP MOP mode, since that was a
standard protocol supported by DEC for this purpose. But it could have been something
custom as well -- it's not something I was ever exposed to.
Yes, as far as I know the 11/05 controller for the VT20 could drive two independent
displays. The VT71 had a single display, the control processor was built into the
terminal case.
I'm fairly sure the VT71 software was derived from that of the VT20, but just how
close they were I do not know.
paul
3:03 p.m.
The VT20 design team was, iirc, John Kirk for the video, and me for
the Unibus interface in the first version. The one with the slick
one shown here,
http://bitsavers.org/pdf/dec/terminal/vt20/vt20_2.jpg
The /05 based package was after my time, I don't remember much about
how it was deployed.
The boot device called using the boot strap board was variable, and I
don't recall anything beyond an RK05
based system (booting the RK) for the versions in the lab on 1-2 in the mill.
It was for the Typeset 11 team, and then the TypeSet.DecSet team/Product line.
bob
On Sat, Aug 10, 2019 at 2:56 PM Paul Birkel via cctech
<cctech at classiccmp.org> wrote:
The DEC VT20 terminal apparently included a PDP-11/05 with a direct mapped
character display and was intended for text editing and typesetting. It
seems to have been followed by the VT21, and then VT71/VT72, all three based
on an LSI-11 (KD11-F). There's a real lack of documentation about these
online, although the VT72 does have a print set.
Apparently the VT20 used the M792-YK as its bootstrap; the Field Guide is
silent regarding the boot device and M792 documentation stops earlier in the
series of variants.
According to the VT72 print set, it used the MRV11-VC (M9942-YC; described
in the Field Guide as a "bootstrap/diagnostic module") for its bootstrap but
is also silent regarding the boot device. In interestingly, the Field Guide
also describes a MRV11-AA (M7942-TB) as a "M7942 with VT52 emulator, VT71
bootstrap".
For async. communications the VT20 used a DL11-B (M7800 (EIA)). the VT72 a
DLV11-F (M8028).
Looking in a DEC "Options and Modules" listing I see VT20 bundles including
Typeset-11 and DECset-11, and it appears that the VT20 could be configured
with two displays & serial lines in a single 11/05.
So . is the boot device in these systems the remote host via the serial
line? What protocol would that have been? Something native to Typeset-11
and DECset-11?
paul
11 Aug
11 Aug
4:45 p.m.
On Sun, Aug 11, 2019 at 1:18 AM Bob Smith via cctalk <cctalk at classiccmp.org>
wrote:
The VT20 design team was, iirc, John Kirk for the
video, and me for
the Unibus interface in the first version. The one with the slick
one shown here,
http://bitsavers.org/pdf/dec/terminal/vt20/vt20_2.jpg
That looks pretty nice, since externally it just looks like a VT05 with
extra buttons.
The vt20/b (photos in same directory), on the other hand, is one of the
ugliest terminals I've ever seen.
4:49 p.m.
I worked on a lot of Xerox 820s, apparently that did the same job!
On 11/08/2019 19:45, Eric Smith via cctalk wrote:
On Sun, Aug 11, 2019 at 1:18 AM Bob Smith via cctalk
<cctalk at classiccmp.org>
wrote:
--
Nigel Johnson
MSc., MIEEE
VE3ID/G4AJQ/VA3MCU
Amateur Radio, the origin of the open-source concept!
You can reach me by voice on Skype: TILBURY2591
If time travel ever will be possible, it already is. Ask me again yesterday
This e-mail is not and cannot, by its nature, be confidential. En route from me to you, it
will pass across the public Internet, easily readable by any number of system
administrators along the way.
Nigel Johnson <nw.johnson at ieee.org>
Please consider the environment when deciding if you really need to print this message
The VT20 design team was, iirc, John Kirk for the
video, and me for
the Unibus interface in the first version. The one with the slick
one shown here,
http://bitsavers.org/pdf/dec/terminal/vt20/vt20_2.jpg
That looks pretty nice, since externally it just looks like a VT05 with
extra buttons.
The vt20/b (photos in same directory), on the other hand, is one of the
ugliest terminals I've ever seen.
5:25 p.m.
On Aug 11, 2019, at 7:45 PM, Eric Smith via cctalk
<cctalk at classiccmp.org> wrote:
On Sun, Aug 11, 2019 at 1:18 AM Bob Smith via cctalk <cctalk at classiccmp.org>
wrote:
It looks a bit like an early concept for what became the VT71. The terminals directory
also shows a thing called VT21 which appears to be identical to the VT71. I wonder if the
VT20/b and VT21 were engineering prototypes that were later released under the name VT71.
paul
The VT20 design team was, iirc, John Kirk for the
video, and me for
the Unibus interface in the first version. The one with the slick
one shown here,
http://bitsavers.org/pdf/dec/terminal/vt20/vt20_2.jpg
That looks pretty nice, since externally it just looks like a VT05 with
extra buttons.
The vt20/b (photos in same directory), on the other hand, is one of the
ugliest terminals I've ever seen. 
10 Aug
10 Aug
8:01 p.m.
On 8/10/2019 1:56 PM, Paul Birkel via cctech wrote:
The DEC VT20 terminal apparently included a PDP-11/05
with a direct mapped
character display and was intended for text editing and typesetting. It
seems to have been followed by the VT21, and then VT71/VT72, all three based
on an LSI-11 (KD11-F). There's a real lack of documentation about these
online, although the VT72 does have a print set.
Apparently the VT20 used the M792-YK as its bootstrap; the Field Guide is
silent regarding the boot device and M792 documentation stops earlier in the
series of variants.
According to the VT72 print set, it used the MRV11-VC (M9942-YC; described
in the Field Guide as a "bootstrap/diagnostic module") for its bootstrap but
is also silent regarding the boot device. In interestingly, the Field Guide
also describes a MRV11-AA (M7942-TB) as a "M7942 with VT52 emulator, VT71
bootstrap".
For async. communications the VT20 used a DL11-B (M7800 (EIA)). the VT72 a
DLV11-F (M8028).
Looking in a DEC "Options and Modules" listing I see VT20 bundles including
Typeset-11 and DECset-11, and it appears that the VT20 could be configured
with two displays & serial lines in a single 11/05.
So . is the boot device in these systems the remote host via the serial
line? What protocol would that have been? Something native to Typeset-11
and DECset-11?
paul
I wonder if, maybe, it used the same protocol as the GT40, which also
had a boot-over-serial line capability.
JRJ
10:46 p.m.
-----Original Message-----
From: Jay Jaeger [mailto:cube1 at charter.net]
Sent: Saturday, August 10, 2019 11:02 PM
To: Paul Birkel; General Discussion: On-Topic Posts
Subject: Re: DEC VT20 boot device
On 8/10/2019 1:56 PM, Paul Birkel via cctech wrote:
That's a promising lead! The GT40/42 User's Guide (EK-GT40-0P-002), Section 5.1
Communications Bootstrap/Read-Only Memory (ROM) describes a 256 word (GT40) and 512 word
(GT42) ROM, however it appears that the bootstrap loader portion is intended to occupy 63
words which fits the M792 capacity (on the GT40 just the absolute addresses 15700-15776
(base 8)).
Section 5.1.1 Bootstrap Loader describes the packed-and-serialized 6-bit "byte"
stream, including some nice diagrams. Section 5.1.2 Character Encoding includes an
illustrated example starting from a pictorialized 8-level paper tape. Appendix D has an
annotated (and unexpurgated) program listing of the full GT40 ROM, including the loader
and Figure D-1 Communications Bootstrap Loader Flow Diagram. Program comments suggest
that a PDP-10 was expected as the host for a GT40. I imagine that the same expectation
would have applied for the earlier VT20?
Appendix E is similar, but for the "scrolling ROM - GT42" which appears to be a
VT05 emulation It includes more conventional loaders as well: RF11, RK11, RC11, RP11,
TC11, TM11, and paper tape. According to the program comments, "the fearsome power
of the 11" is brought to bear :->.
Both loaders are credited to Jack Burness.
If I understand the listings correctly then in the smaller VT20 ROM, presumptively based
on the same code, one would be expected to successfully fall off the end of the ROM into
freshly loaded code that signals back to the host that a successful load has taken place.
In the GT40 with the larger ROM that acknowledgement ("SENDIT") is part of the
ROM itself.
paul
The DEC VT20 terminal apparently included a
PDP-11/05 with a direct mapped
character display and was intended for text editing and typesetting. It
seems to have been followed by the VT21, and then VT71/VT72, all three based
on an LSI-11 (KD11-F). There's a real lack of documentation about these
online, although the VT72 does have a print set.
Apparently the VT20 used the M792-YK as its bootstrap; the Field Guide is
silent regarding the boot device and M792 documentation stops earlier in the
series of variants.
...
So . is the boot device in these systems the remote host via the serial
line? What protocol would that have been? Something native to Typeset-11
and DECset-11?
paul
I wonder if, maybe, it used the same protocol as the GT40, which also
had a boot-over-serial line capability.
JRJ 
11 Aug
11 Aug
12:02 a.m.
Paul Birkel wrote:
I have the GT40 boot ROM assembled on a PDP-10 host and used for booting
by SIMH. There is also a GTLOAD program which translates a PDP-11
binary on the PDP-10 host and sends it to the GT40.
I wonder if,
maybe, it used the same protocol as the GT40, which also
had a boot-over-serial line capability.
Section 5.1.1 Bootstrap Loader describes the packed-and-serialized
6-bit "byte" stream
1959
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