LEE said:
You mean kermit uses a protocol other than TCP? And it'd be a
different protocol being spoken on the wire when you use kermit
instead of telnet to connect to the printer's port 9100?
TCP is the transport layer protocol. TELNET is an application protocol
layered on top of TCP (see ftp://ftp.rfc-editor.org/in-notes/rfc854.txt
and its various companion RFCs). Basically what telnet adds on top of
TCP is a set of conventions for representing newlines and control
characters, and echoing characters locally or waiting for the remote
to echo them and so on. The TELNET protocol is 'close enough' to raw
TCP that people frequently use a telnet client to connect to ports used
for other protocols; it's pretty easy for example to telnet to an SMTP
port
and send mail. But there are times when the extra transformation the
TELNET protocol does to your keystrokes gets in the way.
In particular, TELNET protocol must always represent newline with the
two character sequence CR LF. It happens that PostScript is defined to
accept either CR alone, LF alone, or CR LF as a line ending, and
depending on how the %statementedit device in your PS interpreter
happens to be implemented, the PS executive could wind up seeing
two newlines every single time you hit Enter, and giving you two
prompts.
Also, you'll usually want to turn off local telnet echo so you see only
the
character echoed by the PS executive. There are lots of options that
can
be set on a telnet client and you can get it working close to right,
but at
least on my telnet client there was no way to get a completely raw
connection.
By contrast kermit has a /raw-socket option that does exactly what it
says:
it opens a TCP socket and layers no protocol at all over the top of it.
It sends
your keystrokes over the socket and displays what comes back.
In practice the Adobe interpreter in my printer seems to send LF alone
when
it sends a newline, and it is handy to tell kermit to display LF as
CRLF.
So I have a macro in .mykermrc that just looks like this (aslaksen is
the name
of the printer):
define ASLAKSEN {
set terminal lf-display crlf
set host aslaksen 9100 /raw-socket
output executive\13
input 5 \10PS>
if fail end 1
connect /quietly
}
(set terminal lf-display appeared in C Kermit 8.0.212.)
Kermit does a lot more than serial-port communication these days.
http://www.columbia.edu/kermit/
-Chap
