[Simh] Simulating a GT40

[Timothe Litt]

On 03-Sep-18 11:52, Mark Pizzolato wrote:
>
> Interesting...
>
> I'm a little confused though.  I certainly understand using the GT40 
> as a standalone system to run Lunar Lander.   That's great fun.
>
> Meanwhile, if the GT40 could be some sort of terminal to some other 
> system, how was it connected to that other system?  Serial line via the 
> DL device?
>
> Also, how/where was the LK40 keyboard connected to the system?
> Through the DL device?  Was there more than one DL device?
>
> - Mark
>

The GT40 stand-alone is a toy.  Lunar lander was just a demo.

In real life, the GT40 was used as a(n expensive) graphics terminal
(~$10-15K IIRC), most often for the -10.  CAD systems, such as SUDS and
(e.g. circuit) simulations used it.  You could add arbitrary -11
peripherals, but that wasn't often done - not cost effective.  The host
provides the disks & application computes - the GT40, which is a vector
display + lightpen & keyboard offloads the display.  The GT40 pushes
display list execution to a DMA processor, which is similar to the VB10C
(VR30, & type 340), it executes display lists.  (See the DIS device in
the TOPS-10 Monitor calls manual for details of those devices.)  The
GT40's -11 could provide an additional level of abstraction between the
host & display processor.  Interpolation; step & repeat; managing the
light pen interactions (e.g. drag, draw line, etc).

In addition the GT40 could be located remotely from the host - not quite
office environment, but less of a computer room than the -10.  And while
expensive by today's standards, moving the overhead off the -10 was
worthwhile.  I believe the CAD group had clusters of them talking to the
-10.

It had a long life - about 1972, serviced until 1995.  If you needed the
capability, you could afford it.  But you didn't buy one casually.

For most purposes, the GT40 was superseded by devices like the VT105
(VT100 + b/w graphics), VT125, GiGi, & VT240.  But those are all raster
scan devices - which can't match the quality of a vector display.  And
none of them had a lightpen.

Brochure scans:
https://web.archive.org/web/20060509012428/http://d116.com/dec/gt/GT40-3.jpg
https://web.archive.org/web/20060509012428/http://d116.com/dec/gt/GT40-4.jpg
https://web.archive.org/web/20060509012428/http://d116.com/dec/gt/GT40-5.jpg

More technical info:

http://www.bitsavers.org/www.computer.museum.uq.edu.au/pdf/DEC-11-HGTGA-B-D%20GT40-GT42%20User's%20Guide.pdf

The keyboard uses a ~110 bps 20ma current loop interface.  It connects
to the standard console interface to the 11/05(11/10).  I don't recall
what was done with the output side - but I suspect it was brought out to
the usual molex connector so that standard -11 diagnostics could be run.



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