Hi Kumar,
I've ported the modbus foundation code (http://www.modbus.org/toolkit.php) to CVI compatible code. It's not in a driver format, just CVI code. Mail me directly (forumsni@jattie.co.uk) if you want to discuss this further.
Best regards
Jattie
Jattie van der Linde
Engineering Manager, Software & Automation
TEL Magnetic Solutions Ltd