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

Chuck Harris cfharris at erols.com
Sun Sep 11 00:41:01 EDT 2005

John Miles wrote:
> The unfortunate truth is that GPIB is actually a pretty flaky thing.  It
> seems there is always a certain amount of swing-a-dead-cat empiricism
> involved with getting any complex GPIB hookup to work reliably.
> I can't talk to my Tek 492AP SA unless I turn on the 8566B or the 8657A that
> shares its GPIB bus, for instance, and I am fairly certain that all of my
> hardware and cabling is in good shape.  I've run into many little hangups
> like this over the past few years.  None of them have been showstoppers, but
> none of them have made me think too highly of the GPIB spec as a robust
> communications mechanism, either.

IEEE488 requires all devices on the bus to be on for operation.  Most of the
later bus drivers contain circuits that Hi-Z the bus if the instrument is off,
but not all.  The original spec used open-collecter 7438's to drive the bus,
and they definitely did not behave well when turned off.


More information about the time-nuts mailing list