Weeks had been wasted while the manufacturer asked for the pals, tried
them in their own unit, lost them, and found them again when someone
returned from holidays. I was told they worked over there.
After reading this thread, I ended up with a 74hc123 on a scrap of
veroboard trapping pulses on both channels by using 2 fast pulse
traps.I had about 47k/1uF on each side and had a decent blink from the
pulse.
It transpired I had one of the two pulses required, but that the second
was not to be found. In honour of Murphy's Law I tried the swapping the
inputs to test my pulse trap, but that fixeds nothing.
Armed with this information, I engaged the enemy with my elderly and
tempramental Polar ASA scanner, and found bad signatures on the pal in
question. So one month later, I find myself being polite to the
manufacturer because I need them to blow me some PALs. I feel like
sinking a toe into their corporate posterior and 'jumping up and down at
them' but what's the point?
Recently, Somebody Somewhere wrote these words
> You should be able to trap such pulses with a 74x121/123 monostable.
> Choose a time constant of several hundred ms and connect an LED to it
> or choose a time constant of some us and use your scope. The minimum
> trigger pulse length for the 74HC123 is 14-26ns. Uwe.
>
>
> > I have a fault in my test equipment here centred around AD767 DACs.
> > What you need to know is that the AD767s latch an input with a short
> > negative pulse (as short as 40nS) on the /CS line. I'm not getting
> > this action.
>
> > The pulse appears to come from a Pal. I sent the Pals to the
> > manufacturer who tried them in another unit and they worked all day.
> > I feel I am looking for a voltage level or timing problem.
>
> > I have a 20Mhz scope here and can't see the pulse, or trigger on it.
> > My thoughts turned to building a latch trap - some latch circuit
> > that would come up low and latch high if the pulse appeared. I
> > could then tack this onto the chip, and look for the pulse.
>
> > Such a latch could be made from a 74F<something>. Any thoughts on
> > how to check the level (e.g. does it go below 0.8V) or dwell (does
> > it last 40+nS) with this or something similar?
--
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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