Siemens Simatic s7-1500 Manual page 16

Address space
4.1 Address space
Value status (Quality Information, QI)
The meaning of the value status depends on the submodule involved.
For the 1st submodule (=basic submodule), the value status is not relevant.
For the 2nd to 4th submodule (=MSI submodule), the value status 0 indicates that the basic
submodule parameters have not yet been assigned (not ready).
The figure below shows the assignment of the address space with submodules 1 and 2.
Figure 4-3
16
Address space for configuration as 1 x 16-channel DI 16x230VAC BA MSI
DI 16x230VAC BA Digital Input Module (6ES7521-1FH00-0AA0)
Manual, 09/2016, A5E03485975-AD