UART communication

[Jo-Jo]

I have a PXI test system that I am using to test some custom hardware. A few of the tests require UART data to be sent and received. I have a UART to USB device I can use, but I would rather not depend on hardware outside of the PXI chassis if I can. I have some spare channels on a 6535 that I tried to use to get UART working. Unfortunately, I can't reliably receive long sequences of bytes (I can send them with no problems). I still have budget left to buy additional cards if I need to, but I'm not sure that any of them will allow for reliable UART communication. The big problem I had with the 6535s is that I can't always rearm the task fast enough for each byte, and software timing is too unreliable. I'm pretty sure that I'm going to have the same problem with any other card I pick also.

Is there some way to reliably get UART communication to work using just PXI hardware, or do I have to use some additional hardware (like a UART to USB converter)?

[crossrulz]

How many ports do you need?  Here is a 2 port PXI card from NI: PXI-8430/2.  There is up to a 16 port card also available.

[Jo-Jo]

Unless I don't understand something, I don't think that card will work. I already have an RS-232 port on the PXI chassis I have. RS-232 is not the same as UART though. I looked at the datasheet for this card, and it doesn't seem to be able to support 0-3.3VDC UART communication.

Am I missing something?

[crossrulz]

Where is the serial data coming from?  What is the USB-UART adapter you were planning on using?  That would help us have more context of what you are trying to do.

[Jo-Jo]

The data is coming from some components on a custom board. Here is the usb-UART device I am currently using:

http://www.mikroe.com/add-on-boards/communication/usb-uart/

It is a pretty standard FTDI based device. I am running it at 3.3VDC.

[crossrulz]

One option is to use a "translator" between the UUT and the PXI card I linked to earlier.  I have used an SN74LVCC4245A to translate between 5V and 3.3V logic with a lot of success.

[Jo-Jo]

If I'm going to be using hardware that's external to the PXI chassis, I'll just go ahead and use the USB to UART converter I already have.

I was hoping there was some PXI card I could buy that was capable, but it's looking like that isn't the case.

[Kimchi-Taco]

Hey Jo-Jo,

Can you tell me what UART type you're looking for?  Is it a 16550?  Have you considered taking at the PXI-8421/3?

Thanks,

[Jo-Jo]

Can the PXI-8421/3 even use UART? It looks to me like it is only for RS-232 and RS-485, which is not the same thing, althought they are often translated into each other, so it gets confusing. The logic levels are different though.

I have an embedded device I need to communicate to that uses plain old 0-3.3 UART like you would see on any microcontroller.

[Kimchi-Taco]

Hello Jo-Jo,

If you look at page 1-3 of the PXI Serial Hardware Manual you will see that all serial hardware uses the standard 16550-compatible UARTs.  Regarding your 3.3V requirement there are PCI and PXI express interfaces that you can take a look at here, such as:

1.  https://www.ni.com/en-us/shop/model/pxie-8431-8.html

2.  http://sine.ni.com/nips/cds/view/p/lang/en/nid/207739 

Hope these help!