Even though you call it a USB-Switch, it would seem that you're using a USB-GPIB CONTROLLER. Does Keithley offer it's own version of VISA that you installed? If you have, then in MAX you could try turning on the Tulip Passport(Tools>NI-VISA>VISA Options). The other thing you can try is changind all of your VISA Reads and Writes to do I/O Synchronouusly by right clicking on the functions. It's possible that the Keithley controller or it's version of VISA doesn't support asynch reads and writes. I would also recomend that you contact Keithley to see how they recomend you use it with LabVIEW and NI-VISA.
Message Edited by Dennis Knutson on 04-14-2005 11:50 AM