Path: utzoo!attcan!uunet!husc6!bbn!gatech!linus!mbunix!jcmorris
From: jcmorris@mitre-bedford.ARPA (Joseph C. Morris)
Newsgroups: comp.os.minix
Subject: Re: posting of tty.c
Keywords: shar fix tty.c
Message-ID: <35927@linus.UUCP>
Date: 12 Jul 88 13:26:34 GMT
References: <2827@ttidca.TTI.COM> <833@ast.cs.vu.nl>
Sender: news@linus.UUCP
Reply-To: jcmorris@mbunix (Morris)
Organization: The MITRE Corporation, McLean, VA.
Lines: 23

In a recent article ast@cs.vu.nl (Andy Tanenbaum) writes:
>One question, perhaps somebody can help me.  I sort of have the feeling that
>RS232 port 1 uses vector 12 and port 2 uses vector 11.  Is this correct?
>I have scoured the IBM XT Reference Manual from cover to cover, and--silence.

The "standard" interrupt assignment is IRQ4 for COM1 and IRQ3 for COM2.  Most
async adapters these days come with jumpers to select at least IRQ3 or IRQ4;
some offer a wider choice.  I've never seen a spec for interrupts generated
by COM3 or COM4.

IRQ3, as you thought, is interrupt 11 in the processor, and IRQ4 is interrupt
12.  I verified this by looking at some of my notes, but I think the original
PC Tech Reference publication did have it.  On the other hand, a copy of the
PS/2 mod 50 and 60 Tech Reference does identify the uses of the various IRQ
levels, but doesn't seem to map IRQ level to hardware interrupt number.

An *excellent* reference to the various hardware and DOS interrupts is
available from SIMTEL20.ARPA (via anonymous FTP) in the file
PD:<MSDOS.SYSUTL>INTERRUP.ARC  .  It's been updated within the past few
days to include additional software interrupts (DOS, not MINIX), but
it's still useful in summarizing the interface to the BIOS routines.

Joe