Hi everyone, I am new with programming VISA. As part of my first few tasks, I am learning to establish a USB communication with instruments. From the little research I have done so far, I found that there are two classes of USB devices, the USB INSTR and USB RAW. I have no problem communicating with the USB INSTR device I have got. However, I have not been able to establish a successful communication with my USB RAW device. My first attempt to communicate with this device after installing the driver was by means of the NI MAX. ON querying the device to get its identity, the NI MAX returned an error that reads “VISA: (Hex 0xBFFF0015) Timeout expired before operation completed”. Can anyone please advise me on what to do to clear this read problem? I have attached a snap shot of the NI MAX window showing the error message.

Instrument Control (GPIB, Serial, VISA, IVI)

communication with a USB RAW Device

In response to Syrpimp:

Thanks for that page. I read through it and I don't think it fully applies to this situation. I actively chose not to use line termination characters. Since I have direct control of the USB device firmware, I simply look for a packet to come in to the device and echo the contents back out. USB messages are already packetized, so I can work on the packet level. Also, the firmware is doing nothing but this task, so turnaround is pretty quick and doesn't fall under the "older device" category. Clearly the baud settings don't apply. Finally, I am trying to read back large packets of data (at least as large as I send out except to illustrate the point of the timeout error).

In response to Intaris:

The Write Large Pkt USB sub-vi simply chunks large packets of data (>64 bytes) into packets of 64 bytes for transmission. The OUT endpoint queue size is limited to 64 bytes. I also place a delay of 50ms between each transaction just in case the timeout was occuring on the send side of things. That doesn't seem to help.

All data I send out comes back until I get to packets of around 1000 bytes (sent to the "Write Large Pkt USB" sub-vi). At that point I see a loss of data. I will investigate that further, but am not too concerned yet because data transmission will generally happen in packets of less than 64 bytes at intervals greater than 50ms (typically 1 second). I send small instructions (1-5 bytes) and expect occasional results of up to a maximum of 200 bytes back.