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000343_fdc@columbia.edu_Thu Oct 23 13:07:18 2003.msg
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From: Frank da Cruz <fdc@columbia.edu>
Newsgroups: comp.protocols.kermit.misc
Subject: Re: DSR off ...
Date: 23 Oct 2003 16:56:37 GMT
Organization: Columbia University
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In article <cf6cc183.0310230551.52867e2d@posting.google.com>, icurmt wrote:
: Alright, let me give you more insight to why I am seeing all these
: problems. I am using the Single Board Computer to talk to the
: Microcontroller unit through serial ports. The DTR pin on the SBC is
: hacked to recycle the power on the MCU. Now when the communication is
: initiated, the DTR pin goes high(1) which resets the MCU and
: communication fails. Thats the reason that during "show comm"
: I see that DSR is off. Now when the communication terminates, the DTR
: is turned off (0) which turns the MCU on.
:
: Something which puzzles me is that why is DTR handshaking used here
: even when I am stating in kermit program to use the Xon/Xoff
: flowcontrol. I also tried the RTS/CTS handshaking but the result was
: same.
:
DTR and flow control (usually) have nothing to do with each other.
DTR is a signal from the computer to the modem saying "I am turned on"
and/or "this serial port is open". By definition, when you turn it off,
this supposed to break the connection.
Unfortunately in this case, Kermit is not a general-purpose modem-control
manipulating program. It operates at a higher level. "set line /dev/xxx"
turns DTR on (and in most cases also RTS). Closing the device turns it off.
RTS/CTS are used by the device driver (transparently to Kermit) for flow
control if you have "set flow rts/cts".
CD, CTS, DSR, and RI are incoming signals -- "read only". You can see
them with "show comm" and you can test them with the WAIT command.
The only way in Kermit that you can touch DTR is with the HANGUP command,
which sets DTR low for about 250 milliseconds, then brings it back, which
is how one tells a modem to hang up a telephone connection.
- Frank