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.
-Chuck
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