Hi Dan, we ended up implementing your option 2, but it took a many wasted hours to figure out asynchronous VISA wasn't all it was cracked up to be. The application was a lot simpler to write asynchronously, but we had to junk it and start over. My coding partner was pretty annoyed that I pushed him to get rid of the legacy serial and finally upgrade to LV7.
We also tried two different Serial Configure statements, but I didn't realize that an explicit VISA Open would have helped. It would be great if some of this information was available on the Developer Zone Thanks for your explanation; at least we're somewhat less confused. Jason Dunham SF Industrial Software, Inc. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Sent: Friday, June 04, 2004 2:13 PM To: Jason Dunham Cc: Info LabVIEW Mailing List Subject: Re: Asyncrhonous Serial VISA Jason: The part that's causing problems for you is that you can't have 2 simultaneous asynchronous write/read calls in progress on the same VISA session. So there are 3 solutions I can come up with that might help: 1) Use 2 different VISA sessions. Make sure to explicitly call VISA Open before calling Configure Serial Port, and make sure that 'open duplicate session' is set to True. In this case, make sure you close both session refnums when you are done, with VISA Close. (The default to 'open duplicate session' is False, which lets LabVIEW recycle sessions. But when you explicitly open duplicate sessions, you're in charge of releasing them.) 2) Use the 'VISA Bytes at Serial Port' property node to check for data having arrived, in a loop, before you call VISA Read. That way it won't block in the asynchronous node. 3) Use the 'VISA Wait on Event' function to wait for the 'Serial-Character' or 'Serial-TermChar' event (make sure you enable it first.) before you call VISA Read. Suggestions 2 and 3 are pretty much the same, except the fact that in case #2, you'll need to create a while loop with a sleep, whereas in case #3, VISA basically does exactly that for you. To be honest, the choice of synchronous versus asynchronous I/O is pretty much irrelevant since LabVIEW 7.0 came out. Because each execution system contains multiple threads, synchronous I/O on one thread doesn't prevent other LabVIEW execution paths within the same execution system. It's still useful if, for example, you wanted to read from 16 different serial ports, all in parallel (no pun intended). With synchronous I/O, there wouldn't be enough LabVIEW threads to handle them all simultaneously. But with asynchronous I/O, it works reasonably well. (Yes, this case has come up.) I hope this explanation helps. Dan Mondrik National Instruments |---------+--------------------------------> | | "Jason Dunham" | | | <[EMAIL PROTECTED]> | | | Sent by: | | | <[EMAIL PROTECTED]| | | .nhmfl.gov> | | | | | | | | | 06-04-2004 01:44 PM | |---------+--------------------------------> >----------------------------------------------------------------------- ---------------------------------------| | | | To: "Info LabVIEW Mailing List" <[EMAIL PROTECTED]> | | cc: | | Subject: Asyncrhonous Serial VISA | >----------------------------------------------------------------------- ---------------------------------------| Is anyone having success at running asynchronous VISA calls for serial port reads and writes? I made a simple test VI to read one byte from COM1, and write a continuous stream of bytes out of the same port in a parallel while loop. The write loop stalls until the read command times out. I even tried moving the read to a subvi and changing it's execution system, but to no avail. If I read and write from different ports it the read and write are independent, even if the VISA nodes are set to run synchronously. I'm just not getting the whole asynchronous concept, I guess. I have yet to create a VI which behaves different with sync or async VISA calls. I'm using LV 7.1, VISA 3.1 and Windows XP. Jason Dunham SF Industrial Software, Inc.
