Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!hplabs!otter.hpl.hp.com!hpopd!simonh
From: simonh@hpopd.pwd.hp.com (Simon Hunt)
Newsgroups: comp.sys.atari.8bit
Subject: Re: Help with the serial interface
Message-ID: <40060003@hpopd.pwd.hp.com>
Date: 5 Apr 91 13:52:40 GMT
References: <1991Apr2.202802.1881@mathrt0.math.chalmers.se>
Organization: Hewlett-Packard CCG-PWD, UK.
Lines: 15

Atari published "Technical Reference Notes" for the 400/800 which included

   "Operating System User's Manual"
   "Operating System Source Listing" and
   "Hardware Manual"

This is probably the best place to look.
The serial number for the Tech Ref Notes is (was?) C016555.

Another good source of information is "De Re Atari" written by Chris Crawford
(author of "Eastern Front 1941"), though I don't remember the publisher.

Hope this helps...

S. Hunt.