Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!beartrk!ceilidh!dnichols
From: dnichols@ceilidh.beartrack.com (DoN Nichols)
Newsgroups: comp.sys.3b1
Subject: Re: Need 3b1-end pinouts for parallel interface
Keywords: parallel pinout
Message-ID: <1991Feb21.020949.6819@ceilidh.beartrack.com>
Date: 21 Feb 91 02:09:49 GMT
References: <12347@helios.TAMU.EDU> <1086@tsnews.Convergent.COM>
Distribution: na
Organization: D and D Data, Vienna, VA.
Lines: 39

In article <1086@tsnews.Convergent.COM> ward@tsnews.Convergent.COM (Ward Griffiths) writes:

	[ ... part of original question deleted ... ]

>that has the two correct connectors as well.  Remember, the 
>"more common" DB-25 connector was not used for parallel ports 
>untill the IBM PC came out, with a male instead of female 
>serial connector (female makes a lot more sense to me -- if a 
>pin breaks it's easier and cheaper to replace a cable than to 
>repair the CPU) and a parallel connector that looked like 
>everybody else's serial connectors.  In the early days, I saw 

	In spite of the horror stories that followed in the previous
article, (now deleted) this is one thing that IBM did RIGHT.  (Well, the
serial connector at least -- I still shudder at the use of the DB25 for the
parallel, but that was forced on them by the size of the brackets, and
considerations of board spacing.  (Why didn't they just put cutouts for the
36-pin blue ribbon in the back panel above the keyboard connector.? ) About
the only other ones that did it right are DEC (vt100) and Televideo (970).
(There may be others, and if so, I'm sure I'll hear about them :-)

	The REASON that this is right, is that it distinguishes between DTE
(the terminal/computer) and DCE (the modem).  If you can look at a device
and determine that it is DTE or DCE by the gender of the connector, it saves
a lot of interface problems that need not exist.  If all cables with a
different gender on each end were wired straight through, and all with the
same gender on each end were KNOWN to be a fairly generic null modem
connection, interfacing would be less of an art, and more the simple thing
that it should be.  (Leaving just baud rate, parity, stop bits, 7/8 data
bits, ASCII/EBCIDIC/UNAMEIT to deal with :-)  IEEE-488 has the right idea.


	[ ... lots more deleted - almost as much as I typed :-) ... ]

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