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From: robin@batcomp.austin.ibm.com (Robin D. Wilson)
Newsgroups: comp.unix.aix
Subject: Re: YAASPP Solved!
Message-ID: <4931@awdprime.UUCP>
Date: 23 Jan 91 16:55:01 GMT
References: <1498@msa3b.UUCP>
Sender: news@awdprime.UUCP
Organization: IBM AWD, Austin
Lines: 42

In article <1498@msa3b.UUCP> kevin@msa3b.UUCP (Kevin P. Kleinfelter) writes:
>Recently I posted about a serial port problem.  The gist of the problem
>was that serial ports were going dead, requiring a reboot to activate them.
>
>In the course of diagnosing the problem, we discovered that "pdisable -a"
>did NOT drop DTR to the modems... SOMETIMES.  We did not have HUPCL
>in LOGMODES for the port, but we did have it for RUNMODES.  If someone
>had not logged-in on a port, pdisabling the port did not drop DTR.
>
>In other words, if HUPCL is not set (i.e. "stty -hupcl"), then
>pdisableing a port does not drop DTR.  I assert that this is a bug.
>True or false?

Basically, when you set "-hupcl" on a tty, you are telling it, "No matter
what else I say, don't drop DTR.  (ie. don't hang up and close this port.)"

So no, this is not a bug.  The way around this problem is to add HUPCL to the
"STTY attributes at LOGIN" in SMIT.  (BTW, this will become the default at some
point in the future.)

DTR == Data Terminal Ready, which is a voltage on PIN 20 of the standard
RS-232C DB25 connector.  When this signal is present, it indicates that the
*DTE device is ready to communicate.  Normally, this means that the device
is plugged in and turned on.  When signal is dropped, the *DCE device will 
assume that DTE device has ended the communication (ie. it was turned off, 
the wire was cut, it stopped listening to the port.)

*DTE == Data Terminal Equipment (ie. Terminals, Computers emulating a terminal,
etc.)

*DCE == Data Communication Equipment (ie. modems.)


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