Path: utzoo!attcan!uunet!ogicse!intelhf!agora!billsey
From: billsey@agora.uucp (Bill Seymour)
Newsgroups: comp.sys.amiga
Subject: Re: Question about a 14Mhz Amiga 500
Message-ID: <1990Sep26.200059.11019@agora.uucp>
Date: 26 Sep 90 20:00:59 GMT
References: <1560@hslrswi.UUCP>
Organization: Open Communication Forum
Lines: 46

In article <1560@hslrswi.UUCP> cavedon@hslrswi.hasler.ascom.ch (Gilbert Cavedon) writes:
:(I am posting this request for a friend)
:
:I made this changes on my Amiga :
:
:- Replace the 7Mhz Version of the 68000 with a 14Mhz 68000 using the
:  28Mhz clock provided by the Fat Agnus via a D-Flip-Flop.
:
:I have still some problems; I can't access neither the
:hard-disk nor the floppy. Only the bootblock of a normal disquette is
:read, if you use a NODOS disquette then it works.  
:I think this problem is due to wait states that can't be see by the
:devices when the clock speed is increased.
:
:Does anybody know what to do? Has anybody made the same changes to his
:machine? If there is a program that can solve this problem can anybody
:post it to the net?

	There has been a discussion on this topic a couple of times
before.  What you have to do is generate the syncronous bus signals
yourself. VPA, VMA and E-Clock are expected by the 8520s to be syncronous
to the 7MHz system. Since you're generating these at twice the normal
speed, the timings that the 8520s use are wrong.  The most typical
failure is in the floppy drives. The time between turning the drive motor
on and when you're allowed to write is determined by the 8520s, and
when things happen too quickly there, you run the risk of either trying
to read or trying to write to a drive that isn't spinning quite fast
enough.  If your drives spin up quickly, you won't see the problem.
If your drives spin up slowly, they'd be unusable.  I can't see where
that would affect your HD, but they may be using the slow clocks
somehow...

:Thanx.
:
:+--------------------------------------------------------------------+
:| Gilbert CAVEDON            voice : +41 31 63 12 50                 |
:| Ascom Hasler AG            email : cavedon@hslrswi.hasler.ascom.ch |
:| Berne, Switzerland                                                 | 
:+--------------------------------------------------------------------+


-- 
     -Bill Seymour             ...tektronix!reed!percival!agora!billsey
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