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

[Magnus Danielson]

From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
Subject: Re: [time-nuts] Off the wall: anyone with experienceprogrammingHP3456A? 
Date: Sat, 10 Sep 2005 23:16:59 +0200
Message-ID: <17046.1126387019 at phk.freebsd.dk>

> In message <20050910.231305.55202084.cfmd at bredband.net>, Magnus Danielson writes:
> 
> >Just look in the HP5370B service manual and you see that the GPIB interface is
> >"passive" (i.e. TTL chips rather than LSI chip). It may not be the marvel of
> >modernism.
> 
> Some of the smaller devices, like the VHF switches, the entire GPIB interface
> is TTL and all commands are single byte commands...

Which surely makes things *MUCH* simpler.

> btw: the reason for the limit on number of devices powered down is
> that NMOS/TTL based interface chips tend to clamp the bus to ground.

Which should be compared to the relative strong pull of 48 mA. Some
implementations is not strong enought.

> 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.

Cheers,
Magnus