[time-nuts] Off the wall: anyone with experienceprogrammingHP3456A?
Magnus Danielson
cfmd at bredband.net
Sat Sep 10 21:37:41 UTC 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. :/
Cheers,
Magnus
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