Hi Marcio,
I do not believe there is a downloadable library from the NI Developer
Zone for Modbus in anything but LabVIEW 7.1, but I did find a Knowledge
Base article with a link to an NI Alliance member who seems to do some
work with Modbus.
Do LabVIEW and LabVIEW Real-Time Support Modbus?
I also briefly saw some posts where some customers have found some
Modbus VIs by doing a google search, perhaps this could be successful
for you as well! I hope you are able to find something that fits
your needs, either through upgrading LabVIEW, contacting an Alliance
member, or finding a solution elsewhere.
john m
Applications Engineer