VT420 experiment needed

From: Michael Sokolov <msokolov_at_ivan.Harhan.ORG>
Date: Tue Feb 17 15:10:42 2004

Witchy <witchy_at_binarydinosaurs.co.uk> wrote:

> Keypad Enter just ends the compose sequence,

So after canceling the compose, it does NOT transmit the normal code(s) for
keypad Enter (CR, CR LF, or SS3 M)? Are you sure? Maybe you were testing in a
mode where it sent CR which was invisible? Could you try again with the
terminal set to local mode, display controls? According to the docs (and actual
behaviour on VT320) whenever you press a key outside "normal" in a compose
sequence, it cancels the compose and then the key does its normal action. The
only exception is Delete, which is the key you should press to get out of
compose mode you entered unintentionally.

> Interesting. I've always had my terminals set to 7 bit space parity -
> software needs from many moons ago

I used to use the VT100 mode (and still do on console/test terminals) which has
the same effect of forcing a 7-bit only Universe. In spring of last year I
migrated to using an 8-bit environment on the terminal on my desk in the command
room (one I'm typing on right now) to support Russian. Of course DEC built its
classic hardware during the Cold War and didn't support Russian, but I've hacked
it in. I use a downline-loaded 96-character KOI8-E set for my GR set on output,
and since I don't have the guts to tear the VT apart, get to its firmware ROM,
and Russify the keyboard input firmware, I have instead implemented a hack in
the Berkeley UNIX tty driver to enter Russian in KOI-8 from the VT320 keyboard.

> - but setting it to 8N shows some
> interesting things going on with 'display controls' enabled:

Yup, it's a whole new exciting 8-bit world out there. I was quite excited when
I took a VT3xx out of VT100 mode and put it in its native mode for the first

> Compose key plus keypad:
> 00 = <NUL>

This is the hexadecimal compose feature. The keys of the numeric keypad become
hex digits in compose mode. 0-9 are themselves, PF1-PF4 are A-D, '-' is E, and
',' is F. You can enter any 8-bit character from 00 to FF as two hex digits.

> 11 = nothing

Actually it's XON (^Q), though of course it's normally unseen.

> 22 = "
> 33 = 3
> 44 = D
> 55 = U
> 66 = f
> 77 = w

These are just ASCII.

> 88 = HTS (horizontal tab stop?)
> 99 = '99' stepped like a fraction.

C1 high control characters. According to the manual the terminal only allows
you to enter them if it's set for 8-bit controls in Setup. If it's set for
7-bit controls, the manual says that C1 chars entered through hex compose will
be turned into equivalent 7-bit escape sequences. Can you test (using local
mode, display controls) whether this is actually true?

> Mixing keypad and keyboard keys results in a beep and end of sequence.

OK, the reasonable behaviour, just as I was going to implement in my code.

> With
> parity set to 7S I get slightly different results, but then a lot of compose
> sequences don't work with 7S.

Well, yeah, Compose is basically for entering 8-bit characters. The standard
ASCII main keypad supports all 128 possible 7-bit ASCII characters, so you
should never need Compose or anything else for 7-bit ASCII, unless of course you
are one of those strange people who configure their LK201s for some non-ASCII
national mode.

Received on Tue Feb 17 2004 - 15:10:42 GMT

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