Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!dcl-cs!gdt!gdr!exspes
From: exspes@gdr.bath.ac.uk (P E Smee)
Newsgroups: comp.sys.atari.st
Subject: Re: media change problem with Toshiba drive
Message-ID: <1990Jan5.103650.28987@gdt.bath.ac.uk>
Date: 5 Jan 90 10:36:50 GMT
References: <7193@shlump.nac.dec.com> <1856@ultb.isc.rit.edu>
Reply-To: exspes@gdr.bath.ac.uk (P E Smee)
Organization: University of Bristol c/o University of Bath
Lines: 39

In article <1856@ultb.isc.rit.edu> clf3678@ultb.isc.rit.edu (C.L. Freemesser) writes:
>>
>>	I'm adding a Toshiba ND-352TH-A also known as FDD4216G0D as a
>>	second floppy.  If I leave the media change diode 
>>	(pin 34 ---|<|--- pin 28) out, everything works fine, except of 
>>	course media change is not detected.  With the diode, once the disk 
>>	is removed once it always appears write protected.
>>
>>		1) What is the media change signal really supposed to do?
>>	    	   I guess that really is, what does Atari expect it to do?

The ST does NOT use the 'media change' signal (aka the 'disk inserted')
signal.  It expects the 'write protect' signal to be asserted when a disk
is removed and uses that to decide whether the disk might have been
swapped.

Chinon drive mechs (some models) had this problem.  The cure for the
affected Chinon mechs (which I'll describe in case it helps find a fix)
is to open the disk drive and have a look around.  (KEEP YOUR GREASY
FINGERS AWAY FROM THE DISK HEADS AND ACTUATOR.)  The mechs had two
adjacent and identical push switches.  One was the write protect
switch, pressed down when you insert a disk with the protect window
closed.  Next to it was the 'disk present' switch, pressed down when a
disk is inserted.  (You can see which is which by putting a disk in
while you've got the mech opened up.)  The cure was to put a jumper
across the pins of the 'disk present' switch, so that the drive always
thinks there is a disk in.  Those mechs only report 'write protect' if
there is a disk in -- if they always think there is a disk in, then
'write protect' does the right thing when there isn't one.  (Sounds to
me like, for your mech, you'd need both to nobble the media-change
diode, and the 'disk present' switch.)

NOTE -- This worked for me.  That does not mean I guarantee it will work
for you.  If you even THINK about opening the case of your mech, on your
own hands be it.  Good luck.

-- 
Paul Smee, Univ of Bristol Comp Centre, Bristol BS8 1TW, Tel +44 272 303132
 Smee@bristol.ac.uk  :-)  (..!uunet!ukc!gdr.bath.ac.uk!exspes if you MUST)