Path: utzoo!attcan!uunet!lll-winken!scooter!neoucom!wtm
From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: comp.sys.amiga.tech
Subject: Re: diskette drives
Summary: I think it is a standard 3.5 inch drive
Message-ID: <1371@neoucom.UUCP>
Date: 17 Oct 88 14:38:17 GMT
References: <2435@hplabsz.HPL.HP.COM>
Distribution: na
Organization: Northeastern Ohio Universities College of Medicine
Lines: 24


I looked inside my A1000.  The disk drive seems to be a garden
variety NEC 3.5 inch drive.  Probably any standard drive would
work.  You'd have to get the documentation for both drives to make
sure that you had the feature jumpers set equivalently.

The external 3.5 inch drive includes a PAL chip on a little board.  When
Amigados boots, it sends a sequence over the drive select line.
The drive will return a sequnece.  When Amigados finds a drive, it
can then send a command to allow it to diasychain to the next drive
on the string.  Other than a couple of leads, most signals are
paralleled on the external drives.  I don't have my schematics here
at work, so I don't want to say something dumb about which leads;
it think that it is the motor/on motor/off that is used by the PAL
to figure out which drive is selected.

Once you get past the circuit board with the PAL on it, the drive
unit should be the same as the internally mounted disk.  Note that
the external 5.25 inch disk lacks the PAL, and thus is not
automatically detected by Amigados.  That means that the 5.25 inch
drive has to be the last device, and there can only be one 5.25
inch disk.  You should be able to unplug an external drive from its
case and substitue it for the internal drive.

--Bill