Recently, Somebody Somewhere wrote these words
> > > What do you use the 74BCTxx for? Long lines
> > > or databus, or high current io?
> > The application is an isa card (vintage 1999) and the chip in
> questionj seems to drive a ribbon to other isa cards.
> > The linues are long by modern standards. There are loads of
> buses about the place. It isn't particularly for driving the extra
> milliamp. Speed could well be a factor.
>
> ISA is not very fast but still needs decent signals.
> AT first that was a 4 MHz bus, later 10MHz if
> I remember well. There are several other
> manufacterers with bus logic. They do not
> all use BCT, but other names.
After pci became common it became a bios configurable thing. This is set
up for maximum waits around the place, but still fails. It can be as
fast as pci/2 (i.e. 16.5Mhz) in some setups. But if that fails, you can
slow it. I have run isa at pci/3 for long periods.
>
> 25 cm (I saw your other email) is very long.
> Instead of speed and current, you may be
> looking at impedance and reflection problems.
>
> Can't you get any original BCT logic anymore?
> That would prevent problems.
>
> I do wonder why the original parts broke down.
>
I am looking at a very dodgy scan on the particular part.
This box was bought second hand in England and shipped here. It has
developed some weird faults, which I am currently attacking with some
success. Outstanding issues include an occasional misreading of test
voltages and heat related humours. Travel like that plays havoc with an
old unit like the Pinpoint 1.
I can't get excited about the chip because it is supposed to be capable
of driving 6 driver cards, and it only has three.
If this fails, I intend to sit it into a passenger seat and drive it to
'hospital' in England. I'm not putting it through a carrier again.
And the Polar I'm scanning it with has shown anything up to 7%
difference between two channels on short circuit( which should be
identical); The software crashes, and the serial port is beginning to
take humours. But visually it is actually very good, and it's pointing a
finger at some things and helping me out where I'd otherwise be stuck.
Devices which fail on ASA might actually pass a function test, but
that's where your intermittent faults come.
One driver board I get here has 18V zeners which break down to ~10V
after being overloaded. This means fets won't switch on right, and
all power devices blow. This technology is invaluable for finding this
sort of thing.
Thanks to everyone who exercised themselves on this.
--
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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