[time-nuts] OT: Prologix GPIB and HP3478A...

Chuck Harris cfharris at erols.com
Wed Nov 28 01:38:08 EST 2007

Prologix wrote:
> Hello Chuck,
> It appears that 3478A sends data continuously as soon as it is addressed to
> talk. Since the Prologix adapter is busy processing GPIB data it is unable
> to respond to USB commands. 

I don't think the 3478A is sending anything at all.

If it was, it should be showing some of the annunciators on its LCD display,
like TLK, LSTN, RMT, SRQ, or something.  But it isn't.

I think the Prologix isn't capable of driving the 3478A, logic level wise,
and is waiting in vain for the 3478A to respond to a signal the 3478A cannot see.

There truly is a reason why 488 bus driver chips exist.  Something about the
talker/controller's 220 ohm/330 ohm pull up/pull down terminator spec, and the
38ma pull down spec.

  > One solution is to turn read-after-write off (++auto 0) before connecting
> the adapter to 3478A, and then use ++read command to read one measurement at
> a time. Please see the manual (www.prologix.biz) for ++read command options.

Nope, doesn't work, locks it up on the first ++read command.

> The other option is to set 3478A to one-reading-per-trigger mode using "T3"
> device command. See HP3478 manual (pages 39, 59). Then use the ++trg command
> to trigger the device. ++auto must be set to 1 in this case.

Sending T3 locks up the Prologix.

-Chuck Harris

> Regards,
> Abdul
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Chuck Harris
> Sent: Tuesday, November 27, 2007 7:34 PM
> To: Discussion of precise time and frequency measurement
> Subject: [time-nuts] OT: Prologix GPIB and HP3478A...
> Hi Gang!
> I just bought a Prologix GPIB <-> USB converter model, version 5.00,
> and I am having some problems.  It works fine on some of my instruments,
> but it just locks up when I hook it to an HP3478A DVM.  The DVM is
> known good, and works great with my HP85B (doesn't everything?).
> Basically, if I do any commands that require bus activity, the Prologix
> locks up and refuses to respond to even the ++ver command.  When I unplug
> the HP3478A, the Prologix once again finds its happy spot, and responds
> normally.
> Any ideas?
> -Chuck Harris

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