Re: What is this?

[dempson@actrix.gen.nz (David Empson)]

MA <Marlin.Allred@unisys.com> wrote:
> 
> I have a Macintosh LC which insist that Appletalk is enabled for the
> printer when it is first booted up. Is that normal behavior?

It depends on the printer.  If it is an AppleTalk-only printer, such as
an appropriate LaserWriter model, then yes.

Some printers are able to work with or without AppleTalk, generally
using different drivers.  An example is the ImageWriter II (with
LocalTalk option card fitted).  Flipping a DIP switch is all it takes to
change the connection mode of the printer, and you need to change
between the AppleTalk and non-AppleTalk ImageWriter driver (on the Mac).

[For the purposes of the following discussion, LocalTalk is equivalent
to AppleTalk - it is just a more precise specification of how the
printer is connected to the computer.]

> I would eventually like to share printers between the Macintosh and
> IIGS, but since no one has come up with a AppleTalk printer driver for
> the HP DeskJet printer on the IIGS, I have been trying to find out what
> it takes to turn off Appletalk printers on the Macintosh.

Which HP DeskJet model?  I assume it is a recent one with LocalTalk
support.  The older ones only supported a rather slow serial connection
(or were parallel only, hence useless on a Mac without some kind of
adaptor).  HP also made "DeskWriter" models that could be used with Mac,
that supported a high speed serial connection (not as fast as LocalTalk,
though), and dropped some other features.

> How difficult is to create a Appletalk printer driver for HP Deskjet
> for the Apple IIGS anyway?

The IIgs doesn't need different drivers for AppleTalk and non-AppleTalk
printers, as long as the driver has been written properly and the
printer command set is identical in both modes.  For example, the IIgs
ImageWriter driver can be used with both AppleTalk and Direct Connect
ImageWriters.  This differs from the Macintosh.

The IIgs splits printer drivers into two layers: the "port" driver deals
with how to communicate physically with the printer (e.g. serial port,
parallel port, or AppleTalk), and the "printer" driver just deals with
the specific details of the printer model, such as imaging model,
command set, user interface for page setup/print, etc.

I have written a simple port driver (intended as a diagnostic tool for
identifying a bug in a printer driver), but didn't get very far in an
attempt to write a printer driver (very big task).


There are at least three catches with the theory that a printer driver
can work on either AppleTalk or Direct Connect:

- It is harder to write an AppleTalk-capable driver, as more features of
the printer/port driver interface must be used.  As far as I know, all
existing DeskJet drivers for the IIgs are not up to this task (not that
I've ever tried it myself).

- Some details of the interface, particularly error reporting, are
likely to change.  For example, the ImageWriter II has a "query" command
that reports the printer model and which options are fitted.  This is
only available in Direct Connect mode.  When using AppleTalk, a status
request is required to get the printer state information.

- A separate Control Panel (CDev) needs to be written to let the user
select a network printer of the appropriate type.  Apple's standard
"NetPrinter" CDev only supports Apple's networkable printers
(ImageWriter II, ImageWriter LQ and LaserWriter).  There is no technical
reason (that I know of) which would prevent a third party implementation
of a "NetDeskjet" CDev (for example).  In theory, Apple's CDev could be
patched to add support for other printer types (but you would still need
an AppleTalk-capable driver for the printer).

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand