Repairing a VT240.

Tony Duell ard.p850ug1 at
Sun May 1 07:20:09 CDT 2022

On Sun, May 1, 2022 at 2:57 AM Chris Zach via cctalk
<cctalk at> wrote:

> Looking through the manual I saw that this thing is nuts: It has a full
> pdp11 in there (a T11 CPU) with something like 256kw of memory, 32k RAM
> and the rest ROM chips. Which is impossible, however they built a bank
> switching system into the terminal so the T11 could access more than
> 32kw of memory. Yes, they literally built a MMU just so they could use a
> pdp11.

I find it rather annoying that with that much processor power there is
no way to run a user program on the VT240. Maybe there is, but I can
find nothing about doing that in the manuals.

> The 11 seems to control the basic functions and the graphics modes (4014
> and REGIS/VT220/VT125) through the graphics chip controller which looks
> like the same one on the Rainbow's expansion video board. However there

It's very like the Rainbow colour graphics board. There are a couple
of programmed PALs in the memory update logic and I seem to remember
that the ones in the VT240 and those in the 'bow are either identical
or at least very similar.


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