At 3:23 PM -0400 7/16/03, John Klos wrote:
>Hi,
>
>>  This is what I'm interested in doing.
>>  The 4/600 only has the one data port though.
>>  If I can speak serial instead of LocalTalk over this port, without 
>>an adapter, that would be perfect.
>>  I didn't think this would be possible, but as I've mentioned, this 
>>isn't my area of expertise.
>
>Yes, this does get a little confusing.
>
>Here are some things you can try:
>Find the documentation for your printer and see if it will allow non-Mac
>printers to connect to it via an RS-232 to Apple serial cable. If so, you
>should be able to initialise the port in NetBSD by updating /etc/ttys, and
>you may see something (flashing light, maybe even a page) by just catting
>a PostScript file to that serial port.
>
>Note that most direct computer to printer connections are capable of both
>serial and LocalTalk, but I'm not sure if the printer will listen to
>serial if a LocalTalk connection is sensed. You may need to make your own
>cable which looks to the printer like a regular serial connection. This
>involves converting the connection from balanced RS-422 to single ended
>RS-232 by letting TxD+ float and tying RxD+ to ground on both sides.

Actually I thought it sensed a LocalTalk dongle by something unusual 
done with the handshaking/status lines.  Absent that cross-connect 
(whatever it was) it should treat it like a serial line.

You should be able to use RS-422 signalling for an ordinary serial 
connection if you want.  In fact I don't think the hardware can tell 
if you are doing single-ended (RS-232/RS-423) or differential 
(RS-422).  The only difference is the noise immunity at high speed.

Lest you get intimidated:  the standards specify that you can 
cross-wire *any* wires on the connector *indefinitely* without 
damaging anything.  You've got nothing to lose (except time).
-- 
The opinions expressed in this message are mine,
not those of Caltech, JPL, NASA, or the US Government.
Henry.B.Hotz@jpl.nasa.gov, or hbhotz@oxy.edu