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From: jesup@cbmvax.commodore.com (Randell Jesup)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: Clicking Drives II
Message-ID: <17578@cbmvax.commodore.com>
Date: 15 Jan 91 00:29:33 GMT
References: <1990Dec19.164559.19792@engin.umich.edu> <135@dogmelb.dog.oz.au> <1990Dec20.211301.28307@msuinfo.cl.msu.edu> <7357@sugar.hackercorp.com> <1990Dec31.091243.470@phoenix.pub.uu.oz.au> <1412@tardis.Tymnet.COM>
Reply-To: jesup@cbmvax.commodore.com (Randell Jesup)
Organization: Commodore, West Chester, PA
Lines: 20

In article <1412@tardis.Tymnet.COM> jms@tardis.Tymnet.COM (Joe Smith) writes:
>So, the Amiga can detect immediately when the floppy is removed.  However,
>there is no signal from the disk drive that says when a new floppy is
>inserted.  The only way to detect the presence of a floppy in the drive
>is step the heads to the next track and see if that operation has caused
>the CHNG signal to become de-asserted.

	Almost right.  The Amiga still has to poll to notice a disk removal,
though there's no need to step the head.  It must select the drive, and then
examine the state of the CHNG signal.  Also, due to a few drives we once
used, we have to wait an extra 12us after selecting the drive before examining
the signals, since a manufacturer over-buffered or under-drove them (they
don't move for a long time, then slowly slope down over several hundred ns).

-- 
Randell Jesup, Keeper of AmigaDos, Commodore Engineering.
{uunet|rutgers}!cbmvax!jesup, jesup@cbmvax.commodore.com  BIX: rjesup  
The compiler runs
Like a swift-flowing river
I wait in silence.  (From "The Zen of Programming")  ;-)