VISA read waits for full timeout

[Snamprogetti]

My program does common things with serial port and VISA blocks, such as sending "AT" commands to a modem and receiving "OK" with termination character \n. All is fine on my PC (Labview 2009), but when i run the same executable on another PC (Runtime engine 2009), and connect it to the same modem, the VISA reads take a lot of time, by unnecessarily waiting for the full timeout. No timeout errors, reads are correct, but very slow. It happens only with my program on that PC, the VISA test panel in MAX is fine. What could be the reason?

[Mark_Yedinak]

Can you post your code? I suspect that you may not be terminating your read on the termination characters correctly in the code. Does your actual code work on one PC and not the other or are you comparing the results of MAX with your code?

[Snamprogetti]

It works on one PC and not the other. Looks like some machine-level setting of VISA.

Here's the core of comunication code with termination character, however:

VISA read generates error when termination char isn't received within timeout.

In second PC, it generates no error and the termchar is received... but as slow as possible!

[JÞB]

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Snamprogetti wrote:

It works on one PC and not the other. Looks like some machine-level setting of VISA.

Here's the core of comunication code with termination character, however:

VISA read generates error when termination char isn't received within timeout.

In second PC, it generates no error and the termchar is received... but as slow as possible!

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Check the radix on the "10" int constant!

[Snamprogetti]

It's decimal 10, that's character \n

[Mark_Yedinak]

Is that what your data is terminated with? Are you using XON/XOFF flow control? If so, it will filter out the 0x0A byte since it uses that for flow control. Try using hardware flow control instead.

[Snamprogetti]

Flow control is left to default (0 - none).

Everything i can set in my Labview program is the same in both PCs, except COM port number

[pincpanter]

What about serial hardware?

[Snamprogetti]

The "good" PC has a traditional COM1 port.

The "bad" PC actually has a USB-serial converter, appearing as COM4, but it works fine with terminal or MAX.

The connected modem is the same one.

[Mark_Yedinak]

Have you tried running NI SPy to see what is happening. You have a fairly significant difference once you introduce the USB to serial. They don't all act the same. Can you try running in the second PC using a regular com port and see if that works.