This can be done using DFM. And it is done automatically when the device is managed by DFM depending on what is connected to the ports. If the ports are connected to other devices that DFM is managing, then the ports will be considered trunk ports to DFM, and DFM will automatically report on link down (OperationallyDown) conditions.

If, however, the ports are not connected to other devices which DFM is managing, then you will need to go to DFM > Device Management > Device Details, and launch the Device Details View for this 6500. Choose the ports you wish to manage, and set their Management State to true. Save your changes, then go to DFM > Configuration > Polling and Thresholds > Apply Changes for those changes to take effect.