Why can a device or SCADA send a message and change a coil I have forced?
Issue
An application has coils that have been forced but another device or application can send a Modbus write coil message and change the value.
Product Line
EcoStruxure Control Expert (former Unity Pro)
Environment
Unity Pro v12.0
Resolution
Forced coils, by default, can be written to and changed. It depends on the state of system bit 79 (%S79). If the value of %S79 is False (0), the coil can be written to and the value of the forced coil will change. If the value of %S79 is True (this can be set by the user) the value of the coil will not be able to be changed by a message.