Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!amdcad!sun!pitstop!sundc!seismo!uunet!mcvax!botter!star.cs.vu.nl!ast
From: ast@cs.vu.nl (Andy Tanenbaum)
Newsgroups: comp.os.minix
Subject: Re: AN HISTORIC MOMENT!
Message-ID: <845@ast.cs.vu.nl>
Date: 13 Jul 88 08:52:29 GMT
References: <841@ast.cs.vu.nl| <4926@husc6.harvard.edu>
Reply-To: ast@cs.vu.nl (Andy Tanenbaum)
Organization: VU Informatica, Amsterdam
Lines: 23

In article <4926@husc6.harvard.edu> ddl@husc6.harvard.edu (Dan Lanciani) writes:
>	Actually, the 8250 in the PC works fine at 19200 ...

If Dan has tested it, I believe him. Nevertheless, let us all get out our
IBM PC-XT Technical Reference Manuals and read together starting in the
middle of page 1-200 where it says:

\fBNote:\fR The maximum operating frequency of the baud generator is 3.1 MHz.
In no case should the data rate be greater than 9600 baud.

It may be that the chip actually works at higher speeds, but this is outside
the specification, at the very least.  When I was in college I worked at IBM
in the summer as a programmer to earn money for my college expenses.  At that
time I sometimes programmed the IBM 1401, many of whose instructions had the
format:   Opcode address1 address2.  Some of them only had one address, but
curious fellow that I was, I tried the two address forms, and they all seemed
to do something predictable, and in many cases useful (typically a branch to
the second address).  I thought it was real neat to fill my programs with
undocumented instructions (which may have been model dependent) because it
saved a couple of bytes here and there.  Nowadays I prefer to stay within the
official spec.

Andy Tanenbaum (ast@cs.vu.nl)