RS422 Clock Lines

[Slaxx]

Hello

I'm trying to read a PCM Stream that is send from a measurement system via RS422. The device has two data lines (Data+/-) and two Clock Lines (Clock +/-). I have the Moxa Uport 1250 which converts the RS422 to USB.

So far I've dealt with RS232 and I would know how to decode the Stream once I actually receive the data. But I'm struggling here on what to do with the Clock Lines. Do I have to connect them to the TX Lines of the RS-to-USB Converter? Do I have to generate the Clock Signal myself somehow in Labview?

Thanks for any Pointers to the correct direction.

[GerdW]

Hi Slaxx,

are you in the same team as hauserr?

Do you mind to attach (or link to) specific information about your "measurement system"?

[crossrulz · Accepted solution]

First, let's note that RS-422 defines the hardware requirements (differential pair, etc).  However, if you have clock lines then your device is not using a UART protocol.  Therefore, your Uport 1250 is useless.  You need to find a device that does PCM decoding or use an FPGA board or sbRIO or cRIO (really need that FPGA) to do your own PCM decoder.

[Slaxx]

Ah ok now I understand.

I was assume out of pure naivety that this could be done on any device. Then I guess it's a bigger topic if it doesn't exist already.

[Slaxx]

Ah yes, I didn't know he did a board topic on that. I was assuming that he contacted NI support directly.

My fault then.

But with the feedback of crossrulz I think therefore it would also not be possible with the NI 9871?

[crossrulz · Accepted solution]

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@Slaxx wrote:

But with the feedback of crossrulz I think therefore it would also not be possible with the NI 9871?

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Nope.  The 9871 is for UART communications.  But if you are going with a cRIO, I would go with a 9401 and program the PCM decoder in the FPGA.  It might also be worth making a small circuit before it to convert the RS-422 lines into single ended digital lines.  Something like a TI AM26LV32CDR might do the trick.

[Slaxx]

But shouldn't it then also work with the 9401 installed in a cDAQ and a computer with Labview running which functions as the FPGA?

[crossrulz]

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@Slaxx wrote:

But shouldn't it then also work with the 9401 installed in a cDAQ and a computer with Labview running which functions as the FPGA?

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No.  Why?  Timing.  A PC will not have the determinism you need in order to properly decode this.