Validity of I/O Data
For both incoming and outgoing data, PROFINET devices (Controller and Device) send a status byte in submodule granular form, which marks the I/O data as valid or invalid. From an application perspective, this provider/consumer status ultimately specifies whether or not the data of a submodule is valid. The consumer state is to be understood as an acknowledgement that the data sent has been received by the recipient.
The reasons for an IO PS/CS "BAD" can be the following:
No data exchange with the device
Module missing or has a malfunction