Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!umich!samsung!usc!zaphod.mps.ohio-state.edu!math.lsa.umich.edu!hyc
From: hyc@math.lsa.umich.edu (Howard Chu)
Newsgroups: comp.sys.atari.st
Subject: Re: Drive question
Message-ID: <10664@stag.math.lsa.umich.edu>
Date: 16 Jan 90 17:31:52 GMT
References: <1871@mrsvr.UUCP> <5948@umd5.umd.edu>
Sender: news@math.lsa.umich.edu
Reply-To: hyc@math.lsa.umich.edu (Howard Chu)
Organization: University of Michigan Math Dept., Ann Arbor
Lines: 19
UUCP-Path: {mailrus,umix}!um-math!hyc

In article <5948@umd5.umd.edu> matthews@umd5.umd.edu (Mike Matthews) writes:
>In article <1871@mrsvr.UUCP> krieg@jupiter.UUCP (Andrew Krieg) writes:
>>I have had this weird quirk in my ST system ever since I got it (3 years ago)
>>and I am wondering if it is normal.  I have a 520 ST, a single sided disk and
>
>It is.

More elaborately... There's only one set of data and control lines that
go to both disk drives. A particular drive is chosen by the proper number
(0 or 1) appearing on the drive select lines. (The controller is capable
of addressing 4 floppies, but there are only enough lines on the ST
interface to address 2. Oh well.) In any case, the Motor On command gets
fed to both drives, so both will start spinning. However, since only one
drive's "select" signal will ever be active at a time, the other drive
sits there, the light doesn't come on, it doesn't respond to other
commands, etc...
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