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From: louie@sayshell.umd.edu (Louis A. Mamakos)
Newsgroups: comp.lang.postscript
Subject: Re: Postscript printing small and mirrorimaged!!
Message-ID: <1991Jan8.030758.20714@ni.umd.edu>
Date: 8 Jan 91 03:07:58 GMT
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In article <1991Jan07.165702.26015@cpqhou.uucp> pipkinsj@cpqhou.UUCP (Jeff Pipkins @Adv Dev@SE hou ) writes:

>device I have ever heard of use the Ctrl-D to mark the end of the job
>on parallel or serial channels.  This does not mean that it's part of the
>language -- but it seems to be a part of Adobe's implementation of the
>PostScript language.

No, its an implementation of a communications facility that allows you
to submit jobs to the PostScript interpreter.  In my mind, the
distiction is importatnt.  On an Ethernet attached DEC LPS40, you send
an OP_EOJ (end of job) opcode on the TCP connection to distinguish
between different jobs of the same print session.  Normal PostScript
program text is transmitted to the printer across the TCP connection
using an OP_DATA opcode, for example.

>BTW, the Ctrl-C character (over parallel or serial) "cancels" the current
>job, but I'm not completely sure what is meant by that, nor whether it
>is implemented the same in all cases. 

A control-C character on a serial or parallel printer causes an
"interrupt" error condition for the currently executing job.  On an
Ethernet attached DEC LPS40, you send an OP_KILL opcode as TCP urgent
data to accomplish the same thing.

In the case of status messages, the DEC LPS40 printer transmits
logging and status messages on seperate TCP connecton(s) to one or
more management servers on the network.  It a bit of a different way
of looking at that particular issue, since multiple hosts can submit
jobs to the same printer.

In the case of my personal NEC LC-890 PostScript printer, control-T
doesn't do anything too useful on the parallel port.

If you make a distinction between the PostScript program which puts
marks on the page from the details of how you shove the bits from here
to there, you don't get yourself into too many problems.  Perhaps in
the future, PostScript printer on network can access NFS servers
directly, and we simply give them the name of the PostScript file to
print which resides somewhere on an insititutional filesystem.  

Or perhaps Adobe will implement the 8 bit transparent serial channel
on some PostScript printer products which specifies who to escape link
control character codes.  There's an interesting document on the Adobe
archive server that discusses how this might be done.

The wonderful thing about PostScript is that the applications which
generate PostScript files can be ignorant of the mechanisms used to
print them.

louie