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From: brian@ut-sally.UUCP (Brian H. Powell)
Newsgroups: comp.sys.mac
Subject: Re: Mac+ DTR upside down?
Message-ID: <6440@ut-sally.UUCP>
Date: Tue, 25-Nov-86 13:00:07 EST
Article-I.D.: ut-sally.6440
Posted: Tue Nov 25 13:00:07 1986
Date-Received: Tue, 25-Nov-86 20:24:57 EST
References: <1372@umd5>
Distribution: net
Organization: U. Texas CS Dept., Austin, Texas
Lines: 54

In article <1372@umd5>, zben@umd5 (Ben Cranston) writes:
} Upon                          DTR was:
} Power up                      Positive
} Entry to Mac Kermit 0.8(34)   Negative
} Exit from Mac Kermit          Stays Negative
} Entry to MacTerminal          Negative
} Exit from Mac Terminal        Positive

}with MacKermit and Unix
}Windows either too dumb to close the serial driver or smart enough to use
}the new serial driver csCode=16 csParam=0200 feature to keep DTR from being
}reset when the serial driver is closed.

     I don't know anything about positive and negative voltages or rs422 specs.
I do, however, know a little about the serial drivers.  The reason these
terminal programs act this way is not that they are too dumb to close the
serial driver.  They use the old ROM Serial Driver, which you aren't supposed
to close.  Inside Mac II says "You shouldn't ever close the ROM Serial Driver
with a Device Manager Close call.  If you wish to replace it with a RAM
Serial Driver, the RAMSDOpen call will automatically close the ROM driver
for you."  I'll get back to this in a minute.
     They are also not dumb enough to use the new _Control calls.  These would
only work with the new SERD resources, and most of these terminal programs
predate the new SERD anyway.
     Anyway, back to the DTR problem.  The old SERD and the 64K ROM serial
drivers never negated DTR (logically, I don't know if that means positive or
negative electrically).  The new SERD in the 128K ROM drivers (and their
corresponding resource file for use with 64K ROMs) fixed this "bug".
Furthermore, Inside Mac IV says "In the 128K ROM, a single new Serial Driver
replaces the RAM and ROM Serial Drivers."
     Now about those applications.  Remember that MacKermit is written in
SUMacC, which we all know is the most powerful, complete, up-to-date
compiler for the mac.  (In case you don't know about SUMacC, let me include
a :-) here.)  Since SUMacC predated the first definitive 64K ROM SERD, the
RAM Serial Driver wasn't/isn't supported.  So ROM calls were used.  (Perhaps
this will change when the LightSpeed C version of Kermit is released.)
MacTerminal and other terminal programs usually come with SERD resources
installed, so they issue RAM Serial Driver calls.  Uw tries to survive in a
world where the SERD may or may not be present.  Therefore, uw probably makes
ROM calls and gets to use the new SERD if 128K ROMs are present, but doesn't
mind using the 64K ROMs if you don't have the new ROMs.
     So, that's why some terminal programs don't hang up the phone (negate
DTR) when you quit.

Brian H. Powell
		UUCP:	{ihnp4,seismo,ctvax}!ut-sally!brian
		ARPA:	brian@sally.UTEXAS.EDU

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