Path: utzoo!utgpu!water!watmath!onfcanim!dave
From: dave@onfcanim.UUCP (Dave Martindale)
Newsgroups: comp.dcom.modems
Subject: Re: Getting a Trailblazer's ATtention (Was Re: Trailblazer, flow control, DMF32)
Keywords: telebit trailblazer emulex 19200
Message-ID: <15550@onfcanim.UUCP>
Date: 17 Feb 88 20:35:03 GMT
References: <272@coherent.uucp> <3249@cbmvax.UUCP> <10433@mimsy.UUCP> <14856@oliveb.olivetti.com> <3313@cbmvax.UUCP> <15547@onfcanim.UUCP> <5445@elroy.Jpl.Nasa.Gov>
Reply-To: dave@onfcanim.UUCP (Dave Martindale)
Distribution: comp
Organization: National Film Board / Office national du film, Montreal
Lines: 28

In article <5445@elroy.Jpl.Nasa.Gov> stevo@elroy.UUCP (Steve Groom) writes:
>
>However, I eventually concluded that a simple loop like this
>would not work reliably, no matter how many A's were in the attention
>string.  If, for some reason, the modem becomes confused (like
>selecting wrong rate or something), then simply sending the AT sequence
>again won't help.  The modem needs to be reset or otherwise kicked back
>into autobaud somehow before attempting the retry.
>
>In my testing, I never saw a case where the modem failed on the first
>try and then responded on the second or third.  If it failed on the
>first, it *always* failed on *all* subsequent retries, until something
>was done to the modem (reset or cycle DTR).  My solution was to cycle
>DTR between tries, with the modem configured to reset when it saw DTR
>drop (S52=2).

My Trailblazer is also configured to reset on DTR drop.  It seems that
DTR drops reliably at the end of a call, so the modem is always in a known
state when the next try begins, so the autobaud sequence I posted always
works for me.  The one that didn't work reliably apparently just had too
few A's in it.

However, whether your serial port drops DTR reliably when it is supposed
to is a function of both the hardware and software.  If they aren't
working correctly (and Steve talks about DTR not always coming back up
after using 0 baud), then you may have to use whatever you can get to work.

	Dave Martindale