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Connections timeout in Interactive I/O

Question asked by DavidFabijan on Aug 26, 2010
Latest reply on Aug 26, 2010 by changmeikuan

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I'm trying to connect to an Agilent 4284A LCR Meter. Until now I've been using Vee with Direct I/O commands and everything's been working OK. But I have noticed that I cannot communicate with the device in any other mater. I tried the Interactive I/O application, but it times out on every read (no mater how long a wait time I set), including the *IDN? read (which works fine when sent trough Direct I/O in Vee). I also tried the compiling and running the C idn.c sample program but it crashes on ipromptf . Any ideas on what to do?

Thank you for your time.

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changmeikuan Aug 26, 2010 12:50 AM
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Is the EOL terminator correctly configured in other application?
Sometimes restarting the instrument by power-off then power on again might help

I would suggest to turn on IO Monitor come with Agilent IO Libraries Suite, compare the transaction message details for VEE and other application.

Hope this helps
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DavidFabijan Aug 26, 2010 1:03 AM
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Thank you so much for your reply. I used the Monitor as you adviced and I found that the difference is a few Visa::viSet/GetAttribute calls (I don't think this are of much importance). And a VISA::viLock and viUnlock call. This last 2 seem to be the ones that do the trick. Don't really know how I could simulate them in Interactive I/O (any ides?) but I can use them from the C code and that's what I've been aiming for anyway so this pretty much solves my problem. Thank you again.
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changmeikuan Aug 26, 2010 1:15 AM
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You are welcome. I am just sharing my experience

VISA::viLock and viUnlock is just locking/unlocking the VISA session, so that other VISA session cannot interrupt the running program. Let me describe more. Imagine case below:
1. Program A established a VISA session with instrument Z.
2. Program A send *IDN? to Z.
3. Program B established a VISA session with Z, and send other SCPI command to Z.
4. Program A tried to read back the result from Z.

If A locked the VISA session in step 1, step 3 will failed, B will get a VISA error saying something like cannot established communication, session is locked. Step 4 will run without any error on program A.
If A doesn't locked the VISA session in step 1, step 3 will run, then step 4 will get a timeout.

Unless you have case above, or else I don't think the VISA::viLock and viUnlock caused the issue though.

Another tips, before you run Interactive IO, clear all System error. Perform *IDN? query again, then read the result. If there is still timeout issue, go to check instrument system error which usually is SYST:ERR? (The shortcut is next to Clear History of Interactive IO). You may want to perform few SYST:ERR? to read all error messages.
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DavidFabijan Aug 26, 2010 2:11 AM
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You where right, the problem wasn't in the locks but in one of the SetAttributes, particularly in the TERMCHAR_EN attribute.
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changmeikuan Aug 26, 2010 2:34 AM
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That is the terminator character i.e. EOL. If you wish to know the value, highlight that IO transaction, look into the Buffer details e.g. Buffer's buf value.

Alternatively, In VEE, open Instrument Manager, right click on the instrument and select Properties. Click on Advanced then Direct I/O. Look for the Read Terminator (The Write's EOL Sequence should not impact much but maybe it is good to check too). Then in Interactive IO, click on Options, and check the EOL sequence. Compared that with that in VEE. Set the one in Interactive IO if needed and try again.

Hope you will find the root cause soon
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Connections timeout in Interactive I/O

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