YAASPP Solved!
Robin D. Wilson
robin at batcomp.austin.ibm.com
Thu Jan 24 03:55:01 AEST 1991
In article <1498 at msa3b.UUCP> kevin at 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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