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From: psfales@ihlpe.ATT.COM (Pete Fales)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Accessing com3 or com4 on an ibmpc-at
Message-ID: <1949@ihlpe.ATT.COM>
Date: Sat, 15-Aug-87 11:31:34 EDT
Article-I.D.: ihlpe.1949
Posted: Sat Aug 15 11:31:34 1987
Date-Received: Sun, 16-Aug-87 11:30:55 EDT
References: <1174@pacific.UUCP> <3419@islenet.UUCP>
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 29
Keywords: COM3 COM4 MSDOS


 In article <3419@islenet.UUCP>, jons@islenet.UUCP (Jonathan Spangler) writes:
 > >I have an IBM PC/AT that I currently need to add two more com ports (com3 
 > >and com4).  The card I purchased is switchable for that range ports 3 and
 > >4, my question is, How do I get msdos 3.1 or 3.2 to recognize a com3 or com4
 > >=========================>>>>>>>>>>>>>>Thomas Hutton
 > >                         {ucbvax,decvax,seismo}sdcsvax!pacific!hutton
 > >
 > 
 > You need a copy of DOS 3.3, which, among other things, supports four serial
 > ports.

It is also possible to use an installable driver with earlier versions
of DOS.  I was using one for a while that supported COM3 only, but there
should be no problem writing one for any number of COM ports.

There are two problems with this method:
1) There is not a whole lot of standardization on what ports and interrupts
   get assigned to COM3 and COM4.  This means that you have to be sure
   your hardware and software agree on these points.
2) Because of this lack of standardization and lack of BIOS support for
   COM3 and COM4, you may have difficulty using the ports with any application
   that tries to access the ports using other than MS-DOS system calls.

-- 
Peter Fales		UUCP:	...ihnp4!ihlpe!psfales
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