VT105 – the graphical terminal for MINC

The most important part of a MINC system for sure – the vt105 graphical terminal. Graphical as in wave form graphics – another of those bits of IT history that existed only for a brief period in time, when memory cost was so high that the bitmap based graphics we now take for granted would have been prohibitively expensive.

With its limited storage, vt105 is surprisingly capable, and the combination of graph lines, markers, and shade lines makes for graphs that can be compelling even by today’s standards. And current systems with their abstraction layers between program and hardware might even struggle to show shaded strip charts like the vt105 can.

Information sources
Information about the vt105 is mostly from the EK-VT105-TM-001 manual (as found on Bitsavers) and confirmed by running the ZVTN maindec and the examples from MINC-11 Book 4: MINC Graphic Programming. Also, the base vt100 behaviour of the terminal has been confirmed by vttest.

Unknown/Missing information
None currently identified.

Implementation status
The implementation has been verified to all examples in the MINC-11 Book 4: MINC Graphic Programming.

The current implementation only enables the square graph form as described in EK-VT105-TM-001. Since in the software that is available at this point only the square form is used, it doesn’t seem urgent to also implement the rectangular format.

Some of the base vt functionality has not been implemented:

  • 132 column mode; to add this would be quite complex because it would require a different font – and that would not likely look good at a 640×480 resolution. Of course I could use a higher resolution, but that would then add even more complexity and also require a lot more FPGA resources.
  • inverted screen background, ie. dark letters on a bright background; this would be very easy to add, but I suspect it would look horrible – I never used it back in the day for this reason.
  • soft scrolling; adding would not be trivial but still quite doable, but similar to the inverted background, I never used it back in the day – why slow down a system that isn’t very fast in the first place.
  • hard copy; I’d like to add this, but not sure how it should work yet. Saving a bitmap somewhere seems to make the most sense, but where. Maybe a separate sd card interface for the terminal.
  • keyboard settings – like, setting the repeat rate, the leds for caps lock and scroll lock; this should be added at some point, it’s not that difficult to do – but it would require a change to the ps2 component to allow it to write to the keyboard.
  • the BREAK signal – both transmitting and receiving; shouldn’t be difficult except I’m not sure how to test it yet. On the original MINC it would serve to break to odt, but the pdp2011 don’t have that at the moment.

Note that since the May 30, 2021 update, the vt has been updated to support automatic XOFF/XON, and double width/double height characters.