Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!elroy!hacgate!tcville!sed170!lee
From: lee@sed170.HAC.COM (John Lee )
Newsgroups: comp.sys.amiga
Subject: Re: PPPppppplllleeeeeaaaasssseeee stop clicking
Summary: It's all in the drives.
Message-ID: <271@sed170.HAC.COM>
Date: 22 Dec 88 17:22:36 GMT
References: <742@zehntel.UUCP>
Reply-To: lee@sed170.UUCP (John Lee (ird))
Organization: Hughes Aircraft Co., El Segundo, CA
Lines: 45

In article <742@zehntel.UUCP> donw@zehntel (Don White) writes:
>
>     Can anyone at Commodore tell us why (in detail) the drives click? I know
>  they are looking for disk insertion, but HOW are they doing it and why?

I'm not a Commodore person, but I play one on TV.  :-)

The drives click because they indicate the disk inserted/ejected status (via
the /DISKCHANGE signal line, active when a disk has been inserted/ejected
since the last head step) only AFTER the head has been stepped (click!) either
in or out.  This is stated in the A-W Amiga Hardware manual and in the Amiga
Techical Reference manual.  Now as to why you must step the head, I dunno.
Since /DISKCHANGE is it's own separate signal, there's no reason why it can't
reflect the disk status whenever the drive is selected, which doesn't require
a head step (or by some other non-noisy method).  In fact, wouldn't it be much
easier if /DISKCHANGE was instead an active-on-select /DISKINSERTED?

One quieter method that works on some drives is to try step the head backwards 
from track 0.  This will still activate the diskchange flip-flop but since most
drives can't move past 0, they don't click.  This is done by several Kickstart
hacks out there (NoKlickstart?) Unfortunately, some drives (like my brother's)
will strike a mechanical stop and make an even louder click.

>  Don't all drives have some kind of hardware to tell you if a drive is
>  loaded?  Couldn't drives be kept at one known location (like track 0)
>  where you KNOW there should be SOME information? ANd just do reads with
>  no more head positioning?

It's MUCH faster and simpler to step the head and check /DISKCHANGE than it
is to try to read the disk.

>
>     ?????
>     Don White
>     zehntel!donw
>     Box 271177 Concord CA. 94527-1177
		 ^^^^^^^^^^^^^^^^^^^^^^
Gee, someone from my area (I'm from ZIP code 94518).

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