How can I read a discrete input (DI) point from a ROC?

You need to configure a ROC Plus Numeric Point with the correct Type, Location, and Parameter.

A DI point in a ROC has a Type of 101 and the Parameter that holds the actual DI value is 3 (Status). The Location will depend on your specific hardware.

To read an accumulated value, read Parameter 5 (Accumulated Values) with Type = 1. The Location setting is hardware dependent.

For further information, see ROC Plus Numeric Point.