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Vee Reflector: Passthrough control

Question asked by VRFuser on Apr 29, 1996
Thanks to all who replied to my Vee reflector test. Apparently it
was a great success so now I will try to repost some problems that
never were "reflected".

My first question is how to implement pass through control on the
IEEE488 bus using Veetest and an HP VNA model 8720C.  I want to automate
the built-in power sweep calibration on the VNA, but during the calibration
the VNA needs to be the bus master.  According to the limited documentation,
when the VNA is in pass through control, the current bus master, which in
this case is an HP 745i workstation, temporarily hands control off to the
VNA.  When the VNA is finished with the calibration, it returns control back
to the workstation.  This is my understanding of pass through control. 

I have attempted to do this a few different ways, but all I get is a message
on the VNA that says in effect "waiting for control".  One method I tried
was to send an interface operation command:  SEND MSG TCT, where TCT is
"take control".  Nothing happens, and if I send that command twice in
a row, I get a veetest error:

Internal Error:  System error -128.

It seems like I am a few steps away from the solution.

The other problem I am having concerns Veetest running on the HP 745i
workstation.  The workstation is hooked up to a network.  During heavy
network and IEEE488 bus activity, the workstation often crashes.  I
am certain of the circumstances because it crashed a few times during
automated tape back up.  Actually, the IEEE488 bus was not even very
busy.  I had a Veetest program running that took a power meter reading
every hour and logged the results with the time to a file. Examination
of the log file along with the tape backup report linked the events
together.  Crashes also occur at other random times, and the only thing
that seems to be common is that the crashes occur during heavy automated
IEEE488 instrument control and possibly some disk activity.

My guess is that there is a bus contention problem in the workstation that
hangs the system.  Has anyone else experienced similar problems?

Any help with these problems would be appreciated.

Timothy A. Axness
Applied Physics Laboratory