[time-nuts] Off the wall: anyone with experienceprogrammingHP3456A?

Magnus Danielson cfmd at bredband.net
Sat Sep 10 17:37:41 EDT 2005

From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
Subject: Re: [time-nuts] Off the wall: anyone with experienceprogrammingHP3456A? 
Date: Sat, 10 Sep 2005 23:26:57 +0200
Message-ID: <25810.1126387617 at phk.freebsd.dk>

> In message <20050910.232445.04090152.cfmd at bredband.net>, Magnus Danielson writes:
> >> This is less of a problem with modern CMOS based interface chips.
> >
> >Actually, there you end up in another problem, you power the box through the
> >protection diodes which you really must have for CMOS. So it is really not so
> >much better, just different.
> This doesn't happen in any of the designs I've seen.  They basically have 
> a FET in series with the line and when the instrument is OFF, it is really
> OFF.

OK, then they have done it properly. If you don't... OUCH! We learned the hard
way when we did the first attempts on hotswap. Burned a perfectly nice FPGA
input into a nice little low-impedance short-circuit which happilly ate several
amps. :/


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