Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!van-bc!mdivax1!mitchell
Newsgroups: comp.os.msdos.programmer
Subject: Re: COM1 COM2 interrupt numbers?
Message-ID: <1990Sep13.135146.3204@mdivax1.uucp>
Date: 13 Sep 90 13:51:46 GMT
References: <37363@unix.cis.pitt.edu>
Reply-To: mdivax1!bb29c!mitchell (Bill Mitchell)
Distribution: usa
Organization: Mobile Data International
Lines: 12
Return-Path: <mdivax1!news>
Apparently-To: van-bc!rnews

In article <37363@unix.cis.pitt.edu> zhang@unix.cis.pitt.edu (Hong Zhang) writes:
>
>According to MS-DOS Encyclopedia, on PC the int numbers of COM1 / COM2
>are 12 / 11, while on AT, they are 11 / 12. How do I write a comm
>program for all IBM compatibles?
>
>Thanks in advance.

There is a BIOS data area from 0040:0000 thru 0040:008f, containing
all sorts of interesting stuff.  In particular, the first four words
contain the I/O addresses of COM1 thru COM4, and the next four words
contain the I/O addresses of LPT1 thru LPT4.