Using XY Graph to plot current and voltage

Hi,
I'm making an I-V curve tracer, and am hoping to plot current and voltage measurements I'm acquiring onto an XY Graph in realtime. I'm using Labview 2010 on Windows Vista, with the VISA drivers installed; my acquisition hardware is an Arduino Uno communicating over USB to serial via VISA drivers.
My data is coming in over the serial port formatted like "voltage,current":
237,521
320,402
I've read through the relevant documentation for the graph builder, the 4 samples included with LabView, and quite a few posts on this forum. I modified Jazlan's sample VI to read the current and voltage, and display the values on the front panel - it works just fine. However, when I wire those values to an Express XY Graph builder (and set the 'clear data on each call' property to false) and run the software, it just sort of freezes... I try to stop it, but it keeps running for about 10-20 seconds. The current/voltage values are not updated, nor is anything displayed in the XY graph.
Am I not sending the correct input to the graph builder?
Should I just wire up my values directly to the XY graph by concatenating values to an array, and then clustering it?
Also, on the right border of my case structure, one of the orange squares is not solid - how do I fix that?
any help much appreciated!
imran
Attachments:
block.jpg ‏140 KB
project.vi ‏76 KB

thanks for the tip Tim,
I wired up the stop button to the VISA close block, and now I'm able to run and stop it multiple times without freezing.
1) I know how to add shift registers, but why do I need one? It doesn't seem like I need to pass values from one iteration of the while loop to another...
regards,
imran
Attachments:
project.vi ‏43 KB

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