What can cause a GPIB to be unresponsive

Question

I have a GPIB device that I'm communicating with using a National Instruments USB to GPIB. the USB to GPIB works great.

I am wondering what can cause a GPIB device to be unresponsive? If I Turn off the device and turn it back on it will respond, but when I run my program it will respond at first. It then cuts off I can't even communicate with the GPIB device it just times out.

Did I fill up the buffer?

Some specifics from another questioner

I'm controlling a National Instruments GPIB card (not USB) with PyVisa. The instrument on the GPIB bus is a Newport ESP300 motion controller. During a session of several hours (all the while sending commands to and reading from the ESP300) the ESP300 will sometimes stop listening and become unresponsive. All reads time out, and not even *idn? produces a response.

Is there something I can do that is likely to clear this state? e.g. drive the IFC line?

Answer 1

Since you are using National Instruments hardware you can run NI Trace in the background to check all the commands that is send out from the Program. In the Trace do check the last command and its parameters that is send out from the program that causes the hardware to hang.

You can download NI IO Trace here

Answer 2

There should be a clear command (something like "*CLS?", but dont quote me on that). I always run that when i first connect to a device. Then make sure you have a good timeout duration. I found for my device around 1 second works. Less then 1 second makes it so I miss the read after a write. Most of the time, a timeout is because you just missed it or you are reading after a command without a return. Make sure you are also checking for errors in the error queue in between write to make sure the write actually properly when through.

Answer 3

Even the command *CLS will not work if the device is not listening anymore (which might be the case here). The only way to force resetting the device's interface whatever its status (listening or not) is to send the low-level gpib bus message "Selected Device Clear" (it is implemented by the function "ibclr" of the standard gpib library, e.g. https://www.l-com.com/multimedia/manuals/M_USB-488.PDF page 3-7, but I don't know what is the equivalent in Python). This command is intended to be used whenever a GPIB error occurs, I'm always doing it and never had problems. For this to work well you should also monitor the return values of all gpib calls - usually people don't do it so they are unaware of errors until the program hangs.