DEC VT240 terminal

[Ethan Dicks]

On 8/23/07, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
> I've just bought the base unit (VS240) for a VT240 terminal on E-bay and
> know little about it (OK, I know it's a DEC graphics terminal). Perhaps
> somebody can enlightent me

I can try.

> 1) One site i looked at said a VT240 is a monochrome unit, a VT241 is the
> colour version. Is the only difference the monitor? Can I use a colour
> monitor with my base unit?

Yes.  You just need the right cable.  You can use a VR241, if it's
easier to find in the UK, or back in the day, many folks used an
NTSC-frequency Barco-brand monitor, of a variety that had four BNCs
RGB + Csync).

You could probably use an Amiga-friendly monitor as well, as long as
it takes composite sync, or if you care to break up composite sync to
H and V sync.  There's nothing unusual about the VT240 output.

I _think_ it might even produce sync-on-green, which may be what the
mono output is using.  ISTR you tell it in the setup menu (which you
enter just like a VT220) that you want the VT240 engine to render in
color vs mono.  Check a manual - it should be documented.

> 2) On the back are obvious connectors for an RS232 port (DB25), current
> loop (8 pin mate-n-lock). There's a DE9 labelled 'PR', presumably a
> printer port, also RS232.

I believe it's a printer port, but I am reasonably certain it's not
the same pinout as a PC-AT.  It should be some DEC pinout.

> A RJ11 keyboard socket, I assume an LK201 will
> work here (yes?).

Yes.

> A BNC which seems ot be composite mono video. And a
> DA15 plug, also for a monitor. I assume a VR201 links here, or a V241
> with the right cable. Also, can I connect the keybaord to, say, the back
> of the VR201, or do I have to use the RJ11 on the terminal itself?

I don't recall that part, but I would expect the keyboard to work in
either place.  I doubt anything will be harmed by trying.  Most of the
time, DEC was good about that sort of stuff.

> 3) How much is known about the insides?

Not much, AFAIK.

> Of course I've taken it apart.

Of course you have ;-)

I have as well - I got mine by fixing two dead ones.  One had a busted
power switch (I replaced it with one off the wall at Radio Shack), the
other had bad EIA line drivers and/or receivers.

> On this board, there's an 8085, 2681 (dual serial chip), 8251 (USART,
> maybe used for the keybaord interface), 7220 (graphics chip) -- along with
> what seemms to be much the same circuitry as a Rainbow colour card...

Didn't know that.  Make sense, though - that's what the engineers were
playing with at the time, so I'm sure somebody borrowed a circuit from
across the hall.

> another 40 pin chip, DC310. For some reason this is saying 'processor' to me. Is
> it?

Hmm... I don't know that one off the top of my head.  You already have
a processor in there, or else I'd wonder if that was a T-11.  Perhaps
you have a T-11 in there as well as an 8085.  If so, I'd imagine the
T-11 was the ReGIS engine, and the 8085 does all the I/O.

-ethan