Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!att!cbnewsh!rkl
From: rkl@cbnewsh.ATT.COM (kevin.laux)
Newsgroups: comp.sys.ibm.pc
Subject: Re: COM ports - I am still confused!!!
Message-ID: <1510@cbnewsh.ATT.COM>
Date: 16 Jun 89 16:49:27 GMT
References: <29697@ucbvax.BERKELEY.EDU>
Organization: AT&T Bell Laboratories
Lines: 40

In article <29697@ucbvax.BERKELEY.EDU>, brand@janus.uucp (Graham Brand) writes:
| In article <2073@iesd.dk> kjeld@iesd.dk (Kjeld Flarup) writes:
| >I have noted some questions concerning interrupts and COM ports.
| >First there is a reply to Dave Vasko:
| >		PORT    ADDRESS      INTERRUPT 
| >		COM1	3F8-3FF      IRQ4
| >		COM2	2F8-2FF      IRQ3
| >		COM3    2F0-2F7      IRQ4 ( or IRQ2 )
| >		COM4    3F0-3F7      IRQ3 ( or IRQ5 )
| >
| >I think. because noone seems to know for sure.
|    ^^^^^
| 
| 	Thanks for the useful information, assuming that it is correct! 
| However, previous responses have left me a little confused, I must 
| admit. For example, I have seen the following references to port 
| addresses:
| 
| (foss@iris.ucdavis.edu)
| 3E8 for COM3
| 2E8 for COM4

	This is manufacturer dependent.  Some serial ports cards use 2F0 and
3F0; others use 3E8 and 2E8.  3E8 and 2E8 are the more standard.

| (simon@ms.uky.edu)
| 0040:0000 for COM1
| 0040:0002 for COM2
| 0040:0004 for COM3
| 0040:0006 for COM4
| 
| These seem different to me! Would someone please enlighten me?

	0040:0000..0040:0006 are memory locations in the BIOS data area.
They contain the I/O Port base addresses for the COM ports.  If you wish
the system to be aware of COM3 and COM4, you must stuff the I/O port
addresses into the locations yourself.  Also you must set bits 9-11 in the
2-byte word at 0040:0010 (equipment-list word) to the number of COM ports.

--rkl