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From: breemen@rulcvx.LeidenUniv.nl (E. van Breemen)
Newsgroups: comp.sys.amiga.hardware
Subject: 14 Mhz hack
Message-ID: <1991Apr15.091142.2275@rulway.LeidenUniv.nl>
Date: 15 Apr 91 09:11:42 GMT
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Organization: Leiden University, the Netherlands.
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The last weeks there is a lot of talk (again) about the famous
14 Mhz hack. I have such a hack running for months now. To
help other developers I will reveal some clues. First of all
the AS* is not important for the synchronous board. Just connect it
with the 68000 socket. Most important is the DTACK*. You can look
at the PAK board how it is done. Last but not least: replace the
VPA* and VMA* stuff by a circuit using just DTACK*. In other
words my board doesn't use VPA/VMA: they are not connected to the
14 Mhz 68000. If you have to do VPA stuff just hold the DTACK for
about one E-clock. The only 'bug' (if it is a bug) is that I have
sometimes during the first minute a jumping mousepointer. Dave said
he had encountered this also during his experiments, but couldn't say
what it was. Another hint: use sometimes slower logic, how strange this
may seem sometimes it helps! 
Currently I am working at an asynchronous board for the 68020. So
the synchronous board project has more or less ended for me. The main
reason is the fact that the speed advantage is minimal (1.2 not 1.7 or so)
without cach memory. And the m68020 is becoming cheaper, for about $150
you can build a 68020 board.


Erwin van Breemen
Orega Holland.