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000092_news@columbia.edu _Fri Sep 10 18:21:18 1999.msg
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From: fdc@watsun.cc.columbia.edu (Frank da Cruz)
Subject: Re: TVI955 terminal emulation client for Unix (Linux)
Date: 10 Sep 1999 22:01:10 GMT
Organization: Columbia University
Message-ID: <7rbv36$m39$1@newsmaster.cc.columbia.edu>
To: kermit.misc@columbia.edu
In article <7rbjq8$ot7$1@nnrp1.deja.com>, <davidrice@my-deja.com> wrote:
: I connect to a system that uses tvi955 terminal emulation and I need to
: find a client program that does tvi955 terminal emulation on Unix
: (Linux or Solaris). We currently use ProComm as our win32 solution,
: but we are attempting to come up with a Linux solution.
:
: I found the file /usr/share/terminfo/t/tvi955 which looks like a
: terminfo file on my Redhat 6.0 system, but I can't figure out how to
: use it for client emulation.
:
Is there an FAQ for this group? This question should surely go into it...
UNIX is not DOS, Windows, or Mac OS. A UNIX application, other than an
X server and the console driver, does not have direct access to the keyboard
and screen, and so it is not, in general or in any real sense, possible to
write a terminal emulator for UNIX.
Instead, the console (physical keyboard and "raw" screen + drivers) or the
xterm window give you what amounts to an actual TERMINAL. Its characteristics
are what they are; you can't change them (except you can do some key mapping
in X which can affect xterm).
Now, besides the console and xterm, you can also access UNIX from Telnet,
Rlogin, dialin, or even a hardwired connection from another computer through
the serial port, or for that matter from an actual terminal (VT100, Wyse,
TVI, etc). Obviously, when you come into UNIX this way -- i.e. from a remote
computer or terminal, UNIX applications REALLY have no direct access to
your keyboard or screen.
So the question is not what termcaps you can find on Linux -- that's
backwards. The question is: what termcaps can you find on the system you
are connected to FROM Linux. Then you have to set your terminal type on the
remote system where the application is to match the kind of terminal you
have on Linux, or that you are using to access Linux from.
The Linux console "emulates" The Linux Console. It is its own terminal
type. Xterm -- depending on which one you have -- emulates vt100 or vt220.
If you are coming into Linux remotely, then it's the kind of terminal or
emulator you have locally.
If the application you are accessing does not use termcap/terminfo/curses,
and is truly hardwired to TVI955, then you'll need a TVI 955 or an emulator
for one. Since I doubt that anything like this is available for Linux -- at
least not for for free (it is possible, but not easy, to write a custom
xterm program that emulates some specific kind of terminal not emulated by
the xterms you normally can get) -- then you'll need to access Linux from an
actual TVI terminal or from a PC with DOS or Windows that has a TVI 955
emulator.
Another point about UNIX and terminal emulators that might not be obvious is
that in UNIX the communications function generally resides in SOME OTHER
program, such as kermit, cu, telnet, rlogin, etc. In a typical scenario,
you start an xterm window, and then start (say) Kermit IN the xterm window
and have it make the desired connection. Kermit provides the connection,
xterm provides the emulation. (Ditto if you replace Kermit by cu, telnet,
rlogin, etc.) Kermit also gives you file transfer, character-set
translation, and scripting on the connection. More about Kermit at:
http://www.columbia.edu/kermit/
If you are using xterm, it is possible to change what certain keys send
by using xmodmap. For example, the regular xterm probably does not support
high-number function keys, like F8. So if you need to make F8 send what
(say) a DEC VT220 sends, you can (a) install Xfree86 xterm, which does this
already:
http://www.clark.net/pub/dickey/xterm/xterm.faq.html
or use xmodmap to assign the appropriate sequence to the key.
Remember: Kermit, cu, telnet, and friends can't even SEE the F-keys, arrow
keys, Alt key, etc. This is the price we pay for the cross-platform code
portability and openness of access that UNIX offers us. In Windows we can
write terminal emulators because we can always get at the keyboard and
screen. But Windows does not allow the other forms of access the UNIX does.
So in short: no, there is no Procomm for Linux.
These are tradeoffs.
- Frank