[time-nuts] Prologix VRBOOT error

Prologix support at prologix.biz
Tue Jun 3 20:31:13 EDT 2008

Short version:
Connect USB cable before connecting GPIB, and leave USB connected and

Long version:
On startup, if one of the MCU I/O lines is pulled low, the controller will
enter firmware update mode. As it happens, this I/O line is also one of the
GPIB bus signals. Some instruments seem to have stronger pull-down on the
bus lines than others. The controller may enter firmware update mode, if the
USB cable is plugged in while the controller is connected to such an
instrument. Since the pull-down is passive, this behavior could happen even
if the instrument is powered down when connecting USB.

Hope that helps.


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Matt Ettus
Sent: Tuesday, June 03, 2008 5:12 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Prologix VRBOOT error

On Tue, Jun 3, 2008 at 5:03 PM, Prologix <support at prologix.biz> wrote:
> Hello Matt,
> It appears your Prologix GPIB-USB controller is in firmware update mode.
> Please follow these steps:
> 1. Disconnect USB cable and GPIB cable. If the controller is plugged onto
> instrument, unplug it.
> 2. Connect USB cable.
> 3. Connect GPIB cable, or plug onto instrument.
> Let me know if you have more questions.

That seems to fix things.  Simply unplugging USB isn't enough -- I
have to take it off the instruments as well.

How do I keep from getting into that mode in the first place?  I need
this to work reliably without having to reconnect it several times a


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