Hi,
another utility we have used in the past is portmon which you can download from sysinternals.com
From you description however, you're looking at sniffing information on an pre-existing RS232 setup. RS232 is point to point only, so doesn't allow for branching.
If the communicating port is also the one you have access to, and therefore on the pc, portmon will sit in the background, and capture for everything going on. On a network, I beleive it's also possible to get access to log what goes on on another PC, but that's down to portmon itself which is nothing to do with National Instruments.
Hope that helps
Thanks
Sacha Emery
National Instruments (UK)
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