[time-nuts] HP/Symmetricom 58535A and 58536A
Magnus Danielson
magnus at rubidium.dyndns.org
Wed Nov 4 00:09:26 UTC 2009
Hi Ignacio!
> It reminds me when I was breadboarding a TVB divider for my Rb clock
> project. Once I removed the power to the PIC, but the 10 pps led
> continued blinking at a very low intensity. After minutes of
> stupefaction and a search for a charged capacitor or other power source,
> I realized that the beast continued working powered by the 10 Mhz signal
> !!!
This is a classic CMOS "feature" as the input protection diodes will
provide rectifiers to the supply - oriented in the propper directions.
The interesting thing is that devices can behave as almost properly
functioning, except for rare occasions of not working, which is when
none of the inputs provide the Vcc or GND reference needed.
Also, we had this problem with our early hot-swap boards. I had to teach
our hardware guides about protection circuits that hooked the inputs to
the powerplane and all the caps there, producing a high inrush current
unless the drivers where properly isolated. Once the protection was
designed in we saw no more of those errors. Have not heard about that
kind of problem in the last 10 years now. Power-sequencing in the
connectors is there for a reason in some hot-swap systems.
So, all connections to a circuit is potential power-supplies. Sometimes
it has amusing effects and sometimes it has terrible effects.
Cheers,
Magnus
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