VT131 needs keyboard help

From: Andreas Freiherr <Andreas.Freiherr_at_Vishay.com>
Date: Wed Jan 30 05:03:24 2002

Um, er - my five cents...

Tony Duell wrote:

> Anyway, the CRT looks to be pretty standard. 12", 90 degree deflection,
> modified B7G base, 12V (or so) heater, standard pinout. I would be very
> suprised if a monochrome TV tube with the same parameters (and thus
> similar in other respects) couldn't be got to work here.

I seem to remember from ancient times, when I wrote a graphics "driver"
for a VT125 (ReGIS), that the screen has a somewhat nonstandard aspect
ratio. TV would have 4:3 (4 pieces wide, 3 high), while the VT1xx screen
was something like 8:5 - at least numbers that I never had come across
before. Maybe this just refers to the visible picture, and the tube is
standard though.

Yesterday evening, I dug out the microfiches, and, indeed, there is a
"VT100 Technical Manual", part no. EP-VT100-TM-001, dated "Sep 1980". If
anything out of these two fiches can help you, we'll need to find a way
of scanning them. Reduction ratio is 42:1.

About the keyboard interface, it essentially says that this is async,
full-duplex on a single wire. The kludge is to have either end pull the
line up or down through a resistor. If you tap the center of this
voltage divider, which happens to be the actual line, and know what
level your own side is asserting, you can tell what the other side is
doing with a little OP-AMP wizardry (an analog "computor"? ;-). And,
yes, they use 12V there, so there are sufficient reasons not to connect
this to TTL directly.

The manual also says that once in each vertical period, a status byte is
sent to the keyboard to update the LEDs and to initiate a keyboard scan.
Shouldn't this be visible with a scope? - It might give a hint if the
terminal or the keyboard is broken.

Andreas Freiherr
Vishay Semiconductor GmbH, Heilbronn, Germany
Received on Wed Jan 30 2002 - 05:03:24 GMT

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