Wirt Atmar wrote:
> Rereading my previous reply, I noticed that I really didn't answer Frank's
> comments, thus please allow me to take up a little bandwidth and try again:
>
> Frank Nagy wrote:
>
> >Sorry to say but with my demo copy I had problems with the printing of the
> >bar charts. I tried them on our HP 2562C, on an Epson FX1050, and on a
> Laserjet
> >II P printer. Some features seen on the screen were missing - either the
> values
> >of the X axis or the shadowing - if I could have combined the printouts of
> the
> >three printers then I would have got a perfect graph.
>
> The most likely cause of your problems was due to (i) printer
> incompatibilities [including an incomplete implementation of even the
> low-level version of PCL we used in one or more of those printers (I'm not
> sure that an HP2562 supports much of PCL, and I'm even less sure about an
> Epson)] or
The HP2562 seems to be compatible _from_ _below_ the HP Laserjet. I do
not know the history of the printer languages but I guess there are two
main families descending from the common tree:
0) Somebody invented that [Esc] character must hold a special meaning.
1) The Epson Style: The non-printable characters [000]...[031] are
mixed into the sequences beginning with the [Esc] character. If there
is a variable number embedded into a sequence like line spacing, it is
represented by a _binary_ _character_. Example: [Esc]"$"[018] = line
spacing 18/216 inch.
2) The HP Style: The escape sequences only begin with a special
character and their body consists of normal characters in the range
[033]...[126]. If there is a variable number embedded into a sequence
like line spacing, it is represented by a _decimal_ _string_. Ecxample:
[Esc]"&l6.5C" = line spacing 6.5/48 = 13/96 inch.
Transferring printer files in style 1) there is a real danger of loosing
non_printable characters.
Method 2) result longer escape sequences. People accustomed to the
metric system suffers from the strange motion units (1/n inches, see
above) in both cases.
> (ii) the fact that one or more these printers were connected to a
> PC or a terminal rather than to the HP3000 directly.
>
> Most HP terminals (and terminal emulators) strip out -- without warning --
> certain control characters (NULL, ENQ, or DEL) and do not properly pass these
> characters through the terminal to the slaved printer. While these characters
> may mean something to the terminal, they can also be nothing more than
> graphic bit patterns.
>
> However, this deletion of characters is not universal in all HP terminals;
> some don't do it (e.g., 2645) -- and some of the very old terminals (e.g.
> 2624) were configurable as to what characters would be stripped. Under any
> circumstance, this sort of active remanipulation of the data stream kills
> PCL graphics [which ranges in decimal byte value from 000 (white) to 255
> (black)], but does not severely affect text pass-throughs. Seven bit ASCII
> re-transmitters clearly also do just as much harm, but in different ways, as
> do active lans, repeaters, modems or any device that feels it must listen to
> and modify the active data stream.
>
> Over the years, we found that transmitting PCL graphics through anything
> other than a wire that runs directly from the HP3000 to the printer is likely
> to screw it up -- and with all data corruptions, the corruption is not likely
> to be minor.
>
> While I can guarantee that all of the PCL printing problems could have been
> eventually worked out, it is difficult to express my relief at leaving all of
> that behind. PCL was very slow to download, unreliable to retransmit, of
> minimal graphics quality, exceedingly device-dependent, differently
> implemented on virtually every printer it appeared on, and very resource
> consumptive to the host. But other than for those few faults, it's not bad
> language.
>
Sincerely
Frank
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