First, configure the scanner using the barcodes offered by the manufacturer. This includes setting up the baudrate, data/stop bits, etc, symbology (ie. code 39), pre/postamble, etc..
You can experiment with your barcode scanner using HyperTerminal if you are running Windows.
Now, at one stage in the test, you want the operator to scan a barcode to trigger an event. You can place the serial (VISA) communication within a while loop to wait until there is an event from the barcode scanner. You should have a timeout condition (in case the operator forgets to scan or the scanner does not work, etc..).
But first, you need to experiment with the scanner and be able to read the data (ie HyperTerminal).
The rest is Labview code customized to your needs..
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-JLV-