How fast can Serial go with LabVIEW?

[oldmanXJ]

I have a high speed device that talks 3mbaud/sec via serial TTL.  I can use TeraTerm at 3mbaud and the devices work fine.  I am seeing problems getting the LV code to run at 3mbaud.  Is there a limit on the baud rate you can set?

[Bob_Schor]

I have a colleague who has a similar situation, an extremely high serial Baud Rate (don't remember the number, but an order of magnitude at least about 110000 Baud).  He had no trouble using VISA (I think his interface was through USB).  I can ask him for the details ...

Bob Schor

[nathand]

What sort of problems are you having? The serial communication is basically all handled at a very low level by the operating system regardless of which higher-level software (TeraTerm, LabVIEW, etc) you're using, so it shouldn't make a difference.

[crossrulz]

The problem is likely your code.  Teraterm and Hyperterminal are quite dumb and just read data and display.  If you have any delays or are performing concatinations or logging, that will likely cause over flow issues.

Do you have details on the data format and/or the instrument you are reading from?  Also any code we can analyze would help us help you as well.

[Bob_Schor]

I just heard from my colleague, who was using a cable made by FTDI that has a USB connector at one end and six wires described as TTL +5V RS-232 450 mA that he wired into his microprocessor's Serial Out pins.  The company provides a driver that I gather MAX could see.  This particular device "talks" to NI VISA, and describes itself as supporting Baud Rates from 300 to 3M.  My colleague was running it at 921600 Baud.

I believe this may have been the first LabVIEW VI (or VIs) he ever wrote (with a little help from me).  He's very happy with the result.

Bob Schor

[oldmanXJ]

Thanks for the reply.  RS232 only supports up to 921600.  Past that it has to be TTL.  I was wondering if the VISA Serial vi would allow it to be set to 3meg.  I was fighting a LV bug yesterday and didn't get a chance to debug this.  The existing app has been running for over a year and routinely communicates up to that point in speed.  I told it 3meg and I didn't get a link.  I will be looking at it this morning.

[Ben]

The speed of serial is determined by the hardware used and the driver. See here for a serial device that will support 20Mbaud.

NI Used to sell an serial card where they could change out a chip to be able t get at odd baud rates. In that case I had to tell it "baud = X" if I wanted "baud = Y".

Ben

[oldmanXJ]

Thanks.  The hardware uses the updated FTDI chip and it works fine at 3meg with the FTDI drivers with other software.  I just have to figure out why the LV app isn't working, it works slower but not at 3meg.

[RTSLVU]

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@oldmanXJ wrote:

Thanks.  The hardware uses the updated FTDI chip and it works fine at 3meg with the FTDI drivers with other software.  I just have to figure out why the LV app isn't working, it works slower but not at 3meg.

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You are not using "bytes at port" are you?

Post your LV code.

[JÞB]

There is a upper limit to baud rate that NI VISA can support.  It does change from time to time so, it is important to know which version of NI VISA you are using.  Typically a modern version of NI VISA will operate up to about 2M Baud.