Path: utzoo!attcan!uunet!seismo!ukma!tut.cis.ohio-state.edu!ucbvax!IUVAX.CS.INDIANA.EDU!hess
From: hess@IUVAX.CS.INDIANA.EDU (Caleb Hess)
Newsgroups: comp.laser-printers
Subject: Re: NEC LC890 Pageprinter Shortcomings
Keywords: serial ports NEC service
Message-ID: <50647@iuvax.cs.indiana.edu>
Date: 12 Jul 90 15:50:13 GMT
References: <9007120321.AA28460@crayola.cs.UMD.EDU>
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In article <9007120321.AA28460@crayola.cs.UMD.EDU> borriell@aecom.yu.edu (Frank Borriello) writes:
>absolutely not the case.  In fact it is a TTL port where the signals
>vary from 0 to +5V and not -6V to +6V as RS-232 stipulates.  This is no
			    ^^^^^^^^^^
The last time I looked at the EIA RS-232 spec, it gave a range of
-3V to -20something and +3V to +20something.  I have run into a similar
problem with a QMS-PS800 over a long wire run (about 200') where the
voltage drop on the wire was enough to bring the voltage at the receiver
down close to the threshold.  The QMS is now working just fine with a
short RS-232 cable.  There is nothing wrong with using +/- 5V. for RS-232
drivers if you abide by the cable length recommendations. 

However, if your posting is correct and the printer port is not producing
a negative voltage, then there is something wrong with the printer port -
maybe a blown driver chip, or maybe the -5V supply has failed.  I find it
hard to believe that a manufacturer like NEC would deliberately design
an RS-232 port without a negative voltage source.