Rolf,
Thanks for your help. I switched the Master Holding Register Read to a Master Input Register Read but still get nothing. The slave doesn't seem to care about the unit id. Qmodmaster returns data whether the unit id is 0, 1 or 2. Address hex 100 works well for Qmodmaster so I used 256 decimal in Labview. Tried 100 hex also, just in case. I'm wondering if Labview is finding its way out of the computer at all. There are no messages and no data. The register value window is greyed out. The DATA TYPE tab is greyed out on the Properties window. Any thoughts? Thanks for your help.