visa timeout error

[Andrew Leneway]

I am trying to control an older IEEE-488 device and I keep getting timeout errors. I have changed the timeout time to really high and still get it. I have also changed the number of bytes I'm trying to read and still get the timeouts. I'm pretty sure that it has to do with not getting back termination strings. I however have no clue if this device sends one or if it does what the termination would be. Any help would be greatly appreciated.

Thanks

Andy

[Dennis_Knutson]

You don't mention the make and model of the instrument, the command you are sending, and how you are sending the commands (i.e. LabVIEW, CVI, MAX) and that's pretty important information. There can be several reasons for getting a timeout. You could be sending an incorrect command. Did you verify that the command you first send is in the manual? You could be sending the correct command but incorrectly terminated. Most GPIB instruments do not require anything other than the default EOI that is automatically asserted but older ones require a CR, LF, or both. The only way to know is by looking in the manual. All 488.2 instruments are also required to assert EOI when sending data back and if your instrument doesn't, that also could result in a timeout if you are requesting more data than the instrument has available to transmit. If you are getting nothing from the instrument, I would first look at what and how you are sending the data request command.

[Andrew Leneway]

I am controling a delta design 9010 controler, and i get the errors but in Labview and in max when trying to send visa commands. I have checked the commands in the manual, there are only four. When i am ok the 1st time i send ("RT") but when i read and then do another send i get timeout errors. I have tried using the spy to see what the termination string the controller is sending back. Is there any way i can see this?

[Dennis_Knutson]

Do you get a timeout when you do the read? If so, then it's possible that you need to terminate the RT with some other character and using NI-Spy won't help because the controller is not sending anything back at all. Do you have an electronic copy of the programming manual that you can post or a link to it?

[Andrew Leneway]

yes i do get the timeout error on the read as well. I did find out that it does terminate on a CR LF or EOI. i have tried changing the termination to both CR and LF, still get the error. no sorry i don't have an electronic version just a really old hard copy. Could i try using gpib commands instead of visa?

[Dennis_Knutson]

How did you change the termination? You should attach your VI (if 7.1 or earlier) or an image of the code. If you have a string control/constant whith the command, you have to right click on it and select '\' Code Display to include a \r or \n character.

The GPIB Write does give you the option to change the terminate mode of the write but the VISA Write should work the same if properly done.

[Andrew Leneway]

ok i have figured out alittle more that's going on. It seems as though when i do my read the device is sending the responce in two parts however on the 1st part it's not sending termination. Is there a way i can bring them in together?

[Dennis_Knutson]

I'm sort of just guessing since I don't have the instrument, programming manual, or your code. How many bytes are you specifying when you do the VISA Read? If the instrument asserts EOI at the end of it's data and if you haven't changed anything with the termination character, you can specify some large number for the bytes to read. The VISA Read will automatically terminate when it detects EOI so you will get everything that the instrument is sending.