Re: A2gs to HP DeskJet 500 cable

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

James OReilly <joreilly@smtp.dorsai.org> wrote:

> I recently got a Hewlett-Packard DeskJet 500 ink jet printer.  I currently
> am using a Juki 6100 daisy wheel printer.  The Apple IIgs to Juki cable
> has 25 pins at the printer end, as would an Apple IIgs to DJ 500 cable.  I
> realize that although the cables' printer ends have the same no. of pins,
> they could be wired differently.  Does anyone know if the same cable would
> work for both printers, or would I have to get a new cable for my DJ 500?

If this cable plugs into the serial port on your IIgs, and isn't going
though any kind of converter device, and the plug at the Juki end is a
DB-25 male (i.e. the connector on the printer is the same as the one on
the DeskJet), then it is highly likely that the cable will work with the
Deskjet.

If it was my equipment, I would try it, preferably after doing some
simple continuity checks on the cable to confirm that it is the right
type, or reading the Juki manual to find information on the serial
connector pinout.


The RS-232 standard has two defined types of devices: printers and
"communication devices" (e.g. modems).  The difference between the two
is the direction in which data flows through particular pins.  (For a
DB-25 connector, a printer transmits data via pin 2 and a modem receives
data via pin 2; pin 3 is the other way around.)  A printer and modem can
be connected by a straight-through cable.

Computers don't really fit into this, so the computer generally pretends
to be one type of device or the other.  (The Super Serial Card has a
jumper block that determines this.)

In the case of the Mac, Apple IIgs and ImageWriter serial ports, Apple
very sensibly decided to avoid this confusion by using the same pinout
on all devices, and requiring cables to cross the appropriate signal
lines over.  You still need different types of cables when dealing with
devices which use standard connectors.


Where things get hairy is the flow control signals.  There is no
official signal in the RS-232 standard which a printer can use to tell
the connected device that it is not ready to accept data at the moment.
Most printers get around this by using the DTR signal (pin 20) for this
function (it is supposed to mean "I'm not available any more", e.g. due
to some kind of error condition).  Other printers use a different pin.

The DeskJet uses DTR for flow control.  The Juki might use something
else.  If so, you won't get any data being printed via that cable,
because the IIgs will think the DeskJet is busy, or you might lose data
when the printer tells the computer to stop sending.

It is possible that the Juki uses a completely nonstandard pinout, in
which case plugging the cable in without checking it first could be
nasty.

Let me know if you need more information, e.g. about what clues to look
for in the Juki's manual.

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