DAQ 6229 to be used to measure RS232 serial coms

[James Stigwood]

Hi there

 

I have the above PXI card and I was wondering if could be used to measure Serial lines and decode ASCII/Binary/HEX for example.......

 

Or will I need another comm port.

 

Thanks,

 

James

[hooovahh]

I think you could.  I don't think you would want to but I think you could.  The 6229 is nice that it has 32 digital lines on Port 0 because if you didn't know:

 

Only DIO lines on Port 0 of a 'm' series card can perform buffered digital in or digital out.  Search this page for "Port 0" and you'll see the catch http://sine.ni.com/ds/app/doc/p/id/ds-15/lang/en

 

So we can read a buffered digital line on port 0.  So this means we can setup the timing to read a digital line at 1MHz and read it for 1 second.  Then you will get 1,000,000 values of 0 or 1.  This can be done with finite or continuous reading like an analog input.

 

Now when you get 1,000,000 you will likely have a difficult time understanding what that means as far as serial.  You will need to look up RS-232 specifications to understand things like parity bits, and other communication layer things that will be in your read.  If you can interpret that information correctly you will eventually get the ASCII representation of the message.

 

I've never done this so I can't say if there are other issues that I didn't think of.  But really is all this work worth less then the $13 USB to RS-323 adapter?  Not all of these devices support talking to all serial devices, but they work for most applications.

Edited October 18, 2013 by hooovahh

[todd]

I had to sniff an RS-232 link for a project. An additional RS-232 to USB adapter with only the Rx line connected to an existing com channel worked pretty well. Had to read one Byte at a time instead of term chars to not lose sync. The only problem was I needed better than 1ms accuracy on packet start times with relation to some other signals. I did an analog acquisition of the Tx line at 3x the bit rate. It was pretty straightforward to down-sample to one '1' or '0' per transmitted bit. Then a simple state machine to turn the bits into Bytes.