Path: utzoo!attcan!uunet!munnari.oz.au!comp.vuw.ac.nz!actrix!geoff
From: geoff@actrix.co.nz (Geoff McCaughan)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: 14Mhz Comments
Message-ID: <1990Oct9.230639.9336@actrix.co.nz>
Date: 9 Oct 90 23:06:39 GMT
References: <1164@tau.sm.luth.se>
Distribution: comp
Organization: Equinox Public Access, Christchurch, New Zealand
Lines: 52
Summary:Me too....

In article <1164@tau.sm.luth.se> d89-ahg@sm.luth.se (Anders Hedberg) writes:
> 
> Yes, I've got hold of a 16Mhz 68000 and put it in my Amiga 500 rev 5.??.
> It worked fine.
> I've got hold of a 74F?? that i divided the 28Mhz agnus frequency down to
> 14Mhz. It did'nt work fine. Problems: The 68000 needs to be in the right phase
> compared to the agnus chip, else you will see 10 short and one long flash on
> the powerled. Half the times I started my A500 this happend.
  [stuff deleted] 
> To get rid of the wrong phase problem, I've removed the 28/2 divider and
> installed a 7M XOR ( some other signal ) and got 14Mhz. It worked, but the
> drive didn't.

I tried this (7M XOR CDAC), it worked - but only just, I got endless
guru's

> I divided the E signal by two ( down to normal speed ). Ever stepped the drive

E /2 doesn't seem to work. I also tried 7M /10, this worked @ 7MHz,
but wouldn't @ 14. Does anyone know if the 6:4 m/s ratio of the E
clock is all that important? I also tried (just for something to do)
7M /10 AND E to maintain phase with E, but no go.

I put a 4K7 resistor to ground on the CLK pin of the 68000 and a
ferrite bead on the wire leading to it, this got me starting up
properly more than 80% of the time - sounds weird, but it seems to
help, I guess I was getting some ringing.

If anyone knows a way to get this thing running 100% I'd like to
know about it.

BTW when I get my machine running it goes great - very reliable and
quite a speedup. My hard drives run fine, and two of my floppies are
OK as well (internal 3.5" & external 5.25"), the other one is
hopeless unless I run steprate to slow it down, this helps, but it's
still not 100% reliable, even if I slow the steprate down to 10* the
normal delay, so: is there more going on here than just the head
stepping, what else are the timers screwing up?

Also of interest, QuarterBack, Xcopy and MSH, all work fine on all
my floppies, so it seems that anything that doesn't use
trackdisk.device works.
 
Hope to hear from some more of you hardware hackers soon...... keep
your iron hot!


-- 
-------------------------------------------------------------------------------
Geoff McCaughan        Email: geoff@actrix.co.nz  Phone: +64 3 539545 or 852101
Amiga/Hardware/Unix/Quantum Mechanics Hacker      Phax : +64 3 539567
"Anarchy: Think of it as evolution in action."            ^ NEW ZEALAND!