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From: breemen@rulcvx.LeidenUniv.nl (E. van Breemen)
Newsgroups: comp.sys.amiga.hardware
Subject: 14 Mhz Hack
Message-ID: <1991May10.104421.22314@rulway.LeidenUniv.nl>
Date: 10 May 91 10:44:21 GMT
Sender: root@rulway.LeidenUniv.nl (System PRIVILEGED Account)
Organization: Leiden University, the Netherlands.
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To all 14 Mhz hackers,

I have received a lot of mail lately of people who asked me how I made
the 14 Mhz Hack work. It is very simple, just follow the guidelines of Dave H.
I know, a lot of people think they are smart and can avoid all the stuff
which Dave writes about. But that the is reason why all the boards I have
encountered on the network won't work. They may seem to work for 1 minute,
1 day but sooner or later they will break down. For example I had sometimes 
a jumping mouse pointer. First I couldn't figure it out why it jumped. 
The reason why it jumped is still not clear to me, but it disappeared as
soon as I sampled the DTACK only at the end of S4. Before the end of S4,
the DTACK is not valid. I think that the Amiga can give DTACK for example in
S3 but pull it up again in the beginning of S4. So if you sample DTACK at any
time, you can read an invalid DTACK. The Amiga can do this if it sees that the
processor can't finish the buscycle in time (Dave correct me if I am wrong). 
A month ago, I found another problem. My board broke down, after a lot of
 AND #$..,$bfe001 instructions. This is a read/write instruction with an 
E-clock. First thought: the E-clock emulation is bad. Wrong! I didn't 
synchronize the AS. After the E-clock cycle, the Amiga sometimes didn't 
see a flank for sampling the AS. Result: Guru.
For me the 14 Mhz started as Hack with one Flipflop and a 12.5 Mhz processor.
I ended up with a 16 Mhz processor and 7 chips (no wire needed for CDAC).
This is really a minimal configuration, so all the boards using just 2 or 3 
chips won't work, it is sad but true.
Currently I am converting the board into a SMD version, which will be 
published.


Erwin van Breemen

BTW To the designers: don't publish your board before it works 100%. It
will avoid a lot of anger and disappointment.