Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!julius.cs.uiuc.edu!apple!uokmax!munnari.oz.au!brolga!uqcspe!batserver.cs.uq.oz.au!thyssen From: thyssen@batserver.cs.uq.oz.au (Anthony Thyssen) Newsgroups: comp.sys.amiga Subject: Re: Question about a 14Mhz Amiga 500 Message-ID: <5002@uqcspe.cs.uq.oz.au> Date: 26 Sep 90 00:26:20 GMT References: <1560@hslrswi.UUCP> Sender: news@uqcspe.cs.uq.oz.au Reply-To: thyssen@batserver.cs.uq.oz.au Lines: 33 cavedon@hslrswi.hasler.ascom.ch (Gilbert Cavedon) writes: >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. I am currently doing timing on the CAI chips and can tell you straight out that that is one place a problem lies. The `E' line from the 68000 is clocking at a speed of 1/10 of the incoming cpu clock line This is done so as to insure that the `E' line is less than 1Mhz in speed as the chips that use it can't go above this speed (the CIA) (thay were originally designed for the 6800 1Mhz cpu (like the C64) This means that your CIA's are being over clocked and and if thay are running are timing system events at double speed. The vidio parts of the 2 CIA's is still find as thay use the 50/60Hz clock signal. The Disk drive, and general system timer on CIA-A timer B however is running at double speed - And thus interuping too early. Solutions :- Reprogram the timing interupts! OR half the clock output of the 68000 cpu `E' line. Thanks for letting me blab on.... Anthony Thyssen - (Dragon Computing!) thyssen@batserver.cs.uq.oz.au ------------------------------------------------------------------------------- ``Never argue with a computer.'' -- Avon, Blake's 7 -------------------------------------------------------------------------------