Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!mips!apple!voder!zok!wattres!steve
From: steve@wattres.UUCP (Steve Watt)
Newsgroups: comp.unix.ultrix
Subject: Re: Serial problems on DecStations?
Summary: That +-5v was open circuited.
Message-ID: <432@wattres.UUCP>
Date: 20 Feb 90 17:31:32 GMT
References: <422@wattres.UUCP> <423@wattres.UUCP> <6152@umd5.umd.edu>
Reply-To: steve@wattres.UUCP (Steve Watt)
Organization: Steven Watt, Consultant
Lines: 22

In article <6152@umd5.umd.edu> hans@umd5.umd.edu (Hans Breitenlohner) writes:
>In article <423@wattres.UUCP> steve@wattres.UUCP (Steve Watt) writes:
>>I have discovered why this doesn't work:  If you hang an oscilloscope off of
>>the serial port on the DECStation 3100, you see a voltage swing of -5v to +5v

>Personally, I would consider anything that can not operate on +/- 5 Volts
>broken.  (I assume that is under load, not open circuited).

The +-5 was unloaded.  Loaded, it dropped to about 4.8v, definitely below
the threshhold.  Since +-5 is exactly at the edge of the acceptable band,
I don't think that it is broken.  The intent of the band is for the voltage
drop that occurs on longer wires.

>I would be surprised if your modem was powered from the interface, but 
>if it is, it may be fairly easy to substitute a highere voltage on the
>appropriate line.

The modem (a VenTel Pathfinder 18K) is definitely NOT powered from the
RS232 line.  It comes with a rather large transformer.

Just curious:  Does anybody know of an "RS232 signal booster" of some sort?
Like where to buy one, or schematics or something?

--
Steve Watt
...!ames!claris!wattres!steve		wattres!steve@claris.com also works
Is rm -rf a way to remove high-frequency noise?  (No names mentioned!  :)