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