VISA serial not working right in Windows 7

[spaceman_spif]

Howdy.  I wrote a fairly straightforward VISA serial read and write program in LV 2010.  I use VISA write to send a query through the COM port, then use VISA read to get the response and display it for the user.  I do this for several more addresses, then go back to the first one, and then it continues to loop over and over. It works fine when I run it as a vi on my computer, and it runs fine when I compile it and run the executable from my computer as well.  My computer has Windows XP.

However, when I transfer the exe to a laptop running Windows 7, it either works sporadically, or not at all.  I know LV is installed correctly because a couple other small programs work fine, and as I said this one will occasionally communicate, although usually I'll see the wrong address being displayed.

At first I thought it was my code, but no matter how many different methods I tried, it would always work perfectly fine under XP, but awful under Windows 7. Then I ran into Windows 7 USB and COM port driver issues with a different, nonrelated software program, so now I'm beginning to suspect it may be Windows 7 that's the culprit and not my code.

ETA:  LV is the only program running on the Windows 7 laptop, so I know there is nothing else trying to use the COM port.  Plus, I have shut LV completely off and restarted to make sure LV itself isn't still holding the COM port and that didn't help either.

Anyone else run into something like this?

[GuenterMueller]

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@spaceman_spif wrote:

[...] and as I said this one will occasionally communicate, although usually I'll see the wrong address being displayed.  [...]

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What should I expect from this?  This tells me that it is not related to VISA but the application logic.   

Can you post a snippet of what the app is doing?

BTW: I have not faced any VISA issues between WinXP and Win7 so far.

[spaceman_spif]

I'll post a snippet as soon as I can.  It will be messy, but I usually clean it up once it's working nicely.

But in the meantime, I still wonder - if it's my code, then why does it work perfectly fine every time I run the exe from my XP computer?  Plus I've gone throught about 10 different variations of my code and I see the same thing.  The exe works perfect under the XP laptop, but boogers up when I put it on the Win 7 laptop.

[Dennis_Knutson]

What brand of USB-RS232? Have you checked to see if there is a newer driver available for it?

[spaceman_spif]

Actually my LV code is talking through a standard DB9 COM port.  It was another software application I use that communicated through a USB-to-COM converter that I found worked fine via plug-n-play in XP but I had to go through multiple steps to finally get it to work under Windows 7.

Here's a sample of my code.  This is step 4, so I've already established my COM port settings earlier.  It sends out a query, in this case "MD 8009", and the microprocessor will echo back the query plus a value, like "MD 8009 75".  The serial communication in this device is very slow, so I send the message, then I have to loop for a while until I see a response that includes the original string plus more data.  If I don't see a reply that looks correct after so much time, I try sending the query again 20 more times before I give up and flush the I/O buffer then move on to the next address.  If everything works well, I store and display the data, flush the I/O buffer, then move on to the next query.

[spaceman_spif]

I just did a check on the Windows 7 laptops and they have the latest COM port drivers.

[GuenterMueller]

Your receive loop expects to read the entire answer in one loop iteration. I have never dared this but always used a concatenate string to collect the bytes received and then operate on this answer. This I usually accomplish using a Feedback Node or a Shift Register.
I would also add a 1ms wait to the receive loop in order to guarantee that the loop doesn't finish too early.

[spaceman_spif]

Can you post an example on how you read it one byte at a time?  I'm curious if that might work in my case, since I'm expecting a complete string plus terminating character when I'm doing the read function.

[RavensFan]

Why are  you writing to the terminal called "OTT" and a local variable of that terminal at the same time?

[spaceman_spif]

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@RavensFan wrote:

Why are  you writing to the terminal called "OTT" and a local variable of that terminal at the same time?

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Yeah, I know they're both wired there.  This is an early version of my code that I haven't cleaned up yet.  The "OTT" local variable will be used elsewhere, and as soon as I get the code working properly I'll clean up spots like that.

Btw, congrats to your Ravens!!  We'll see if my Bengals can dethrone you next season!!  Unlikely, but hey I can dream can't I??