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From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: comp.sys.amiga
Subject: Re: mount vs. 3.5" drives & diskchange
Message-ID: <641@neoucom.UUCP>
Date: Mon, 27-Jul-87 08:57:11 EDT
Article-I.D.: neoucom.641
Posted: Mon Jul 27 08:57:11 1987
Date-Received: Thu, 30-Jul-87 04:20:47 EDT
References: <13964@watmath.UUCP> <2146@cbmvax.UUCP>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 46
Summary: Drives have a PAL chip


You can order the Amiga schematics from the C-A people in West
Chester, PA.  I can't find the price right now, but it is around
$25.  C-A accepts only check or money order.  The address is
Amiga Technical Support
1200 Wilson Dr.
West Chester, PA  19380

The phone # I have on file is 215-431-9100, but I'm not sure that
it is current.

There is a PAL chip on the drive interface board.  It does at least
three things I know of.

1.  The motor control lead is broken down into two signals:  motor
on and motor off.  These basically toggle a flip-flop on and off to
save the state of the motor

2.  The dirve's media change lead sets a flip flop, so that if the
O/S is busy doing something else when the user swaps disks, that
the event is not lost.  The motor step lead is used to clear the
disk change output.

3.  The PAL can be polled by pulsing some of the inputs (forget
just which ones at the moment).  The PAL puts out a 32 bit device
ID code so that the O/S knows what sort of drive it is.  This is
done when DOS boots.  That's why a 1050 5.25" drive must be
switched on before booting, else DOS won't know it's there.

Other than the above exceptions, my best recollection is that the
rest of the drive signals are off-the-shelf.

Note that the little 1040 (or whatever the # is) 3.5 inch
drives block DC power to subsquent drives in the string.  The
purpose being to prevent some idiot from plugging in 18 drives and
sending his/her Amiga's power supply into a core meltdown.  You can
add more than one external drive by supplying it 5 and 12 volts
from one of those wall-dongle type power packs.  A while back Radio
Shark had some left over from the Coleco Adam or some other brain
damaged marketing attempt; you may still be able to pick one up
(power pack, that is).

Hope this gives you a few ideas,...

Bill
(wtm@neoucom.UUCP)