On Sun, 26 Jul 1998, citadel wrote:
> >I've had serious problems with the 500KHz clock in Nemesis, and had to
> >replace it with a home-made made of a 32MHz oscillator and a
[...]
> I was a bit confused when you mentioned this in an earlier mail as well.
> 500KHz clock? All I can see is 40MHz and 5OMHz oscillator crystals? I
> don't see any 500KHz unit? Can you please explain? As I've said the
The two ACIAs in the Falcon are serial devices, i.e. they communicate
with the keyboard and (naturally) midi-devices over a serial line. The
500KHz clock is used to generate the baud-rates, and it's generated by
dividing the the 32MHz clock by 64. When the system-clock is changed
the 500KHz-clock won't be 500KHz anymore, and the ACIAs won't be able
to communicate with their devices anymore. That's why you have to cut
& lift pin 3+4 on the keyboard- and midi-ACIA and connect them to the
Nemesis which produces it's own 500KHz.
The Nemesis generates this clock by dividing the Falcon's original
clock with a counter of some kind. On both mine and a friends Nemesis
this clock was broken after a while (the same happened with my Speed
Resolution Card), and we had to make our own by dividing a 32MHz clock
with a 74HCT4024 (counter). This works exceptionally well, and we've
had no problems since that.
Btw. we chose to use separate 32MHz oscillators, and not the Falcon's
original clock for this. The Falcon-clock isn't exactly 32MHz, but
IIRC 32125KHz, so the 500KHz-clock won't be exactly 500KHz here
either. The difference is *very* marginal (2Hz) though...
However, I don't think this is your problem. When the clock-divider
broke on my Nemesis, the Falcon got very unstable, with the mouse and
keyboard going crazy, and eventually a complete crash/freeze. Btw. it
appears that this can happen if the Nemesis gets too hot as well, so
you might check the cooling.
> more than this..almost like it's doing things to the system that no other
> program does...something not too kosher? Something that is acceptable
> in a "normal" Falcon but pushes a modified one a bit too hard? I'm just
> guessing, you understand. Thank you so much for all this valuable help.
I'm still convinced that it's your DMA clockpatch that's the problem,
and that you have to experiment further. However, if you're going to
install an Afterburner then you'll have to modify the DMA-patch
again...
/*
** Jo Even Skarstein
http://www.stud.ntnu.no/~josk/
**
** beer - maria mckee - atari falcon - babylon 5
*/
Received on sø. juli 26 1998 - 19:03:28 CEST