visa usb speed

[elxemita]

  Hello. I'm making an application with a PIC and labview communicated via USB 2.0.

[elxemita]

 I am using visa read for get the data. I am sending with high speed the data in a while bucle from my device, and labview doesn't read all the data, it reads slower than i am sending, in order of ms like a COM port. Why can be happening?

[JaimeC]

hi,

You can take a look at:

http://forums.ni.com/ni/board/message?board.id=140&message.id=8184&requireLogin=False

So that would not be a problem.

How much data are you reading each time (bytes)? Probably the problem is the way you ar reading the data... i mean, Windows is not as fast as you should think and for example if you have the read in a while loop and you read 8 bytes the first time the VISA Read subvi is executed you get this 8 bytes. Then you make the while loop and then return to your function. Till that moment windows could had spend 1 or 2 ms.

Solutions:

Did you tried to read more data each time???

Did you inserted a VISA Set I/O Buffer Size VI after the VISA Open ????

Regards,

Jaime Cabrera

NI Applications Engineering

[cris]

Hi,
I'd like to do the same thing....but till now I have been developing applications with pic and  labview which communicate each other via rs232, but now, with the new laptop, i haven't the serial port and the USB -to-rs232 converter is not working well.
May you help me :womansad: with an example in which the communication with PIC and LabView is via USB?
Should I use always NI-VISA as for rs-232 communication?
Thanks a lot


Cristina
Italy

[Wayne.C]

Cristina,

Which USB-RS232 adapter are you using?  Some perform much better than others.  I have had very good luck with adapters from black box and NI.  My testing also showed that a PCMCIA-RS232 adapter was almost twice as fast as a USB adapter.

Stick with the VISA functions for communications.

wayne

[cris]

Thanks for your answer!!

I'm using a manhattan USB-to-rs232 adapter....

At which baud can you succeed in sending and receiving your data?

And for PCMCIA-rs232 adapter which one do you suggest?

thanks

Cristina

[Wayne.C]

Cristina,

I've not had any experience with that adapter.  The fastest baud rate I have used in LabView with a USB adapter is 19200.  Most of my instruments just are not that fast.  The real speed killer has been the time it actually takes to access and read the buffer on the USB adapter.  I have modified my code to reduce the number of VISA reads and maximize how much data I read from the buffer each time.

I have used the NI USB-RS232 adapter with other software packages at speeds above 56K. 

The PCMCIA adapter I'm using is from Black Box.  Picked it up used for $20.  The USB-PCMCIA adapter from NI should be a good one as well.  Maybe another NI user out there has experience with other adapters.

[GcDago]

Dear Cristina,

I'm trying to use a Manhattan USB serial port but I have some problems.

I've installed the driver but I don't see the port on the Measurement and Automation therefore I presume that it can not work. The port is present on the Window Manager.

What's wrong with my procedure?

Thank you for your attention

GcDago

[cris]

Dear GcDago,

I had some similar problem, but I remember it was a driver question. Try to disinstall everything and then sure that you install the right driver for your operating system.

Bye

Cris