On Fri, May 07, 2004 at 02:04:20PM -0800, Dave Baldwin enlightened us
thusly
> > > That may take a lot to get that idea to work. Lots of variation
> > > in that process.
> >
> > If I did the following:
> >
> > 1. Got away from the xtal, and stayed with the reduced clock usually
> > available on pin 20 or 22 of the eprom,
> >
> > 2. got away from powerup and just used watchdog resets
>
> Well, actually, you can't get away from power-up reset when you turn
> the power on. Because many micros have dynamic cells inside instead
> of static. The charge pump for biasing them has to start operating
> and the cells have to be initialized. When you first turn the power
> on, you're dealing with the Analog part of the digital device.
I am not getting away from powering on, but I can avoid testing in that
situation by resetting on a watchdog timer. But are you telling me
that uPs in general _presume_ a power up reset even when the reset might
be from the watchdog? Bah!
>
> > Then I would have a high on the reduced cpu clock ( 'E' or pin 64 on
> > the HD6303XP & HD6303YP) until the xtal was set going. The time
> > between end of reset and first clock cycle would be immaterial. The
> > start of my scan would be the start of the first read cycle.
> >
> > What I really wanted to avoid was having to stick a clip on the
> > eprom and trap an opening read at a low address to get the start
> > signal, and processing also to get a stop.
>
> That's the only reliable way that I can think of to do it. That first
> read is the signal that says the processor is up and running. ??
Then I have to presume the integrity of the address bus. If I can't get
0x0000 hex on the address bus, I can't begin. Mind you, if a board is
that badly shot, I'd probably find heat somewhere.
Then, let's think: Another settable address, or a presettable number of
clock cycles for the stop signal? Mebbe factor in ram & rom checks.
/tries to think it out. fails.
Better do both cycle count and address recognition for the stop to be
sure to be sure. The quest for stability begins.
--
With best Regards,
Declan Moriarty.
--
Author: Declan Moriarty
INET: [EMAIL PROTECTED]
Fat City Hosting, San Diego, California -- http://www.fatcity.com
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