Siemens Simatic series Manual page 25

Parameters/address space
4.2 Address space
Address space for configuration as 1 x 16-channel DI 16x24VDC HF MSI
The channels 0 to 15 of the module are copied in up to four submodules with configuration
1 x 16-channel module (Module-internal shared input, MSI). Channels 0 to 15 are then
available with identical input values in different submodules. These submodules can be
assigned to up to four IO controllers when the module is used in a shared device. Each IO
controller has read access to the same channels.
The number of IO controllers depends on the interface module being used. Please observe
the information in the manual for the particular interface module.
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 0 indicates that the value is
incorrect.
For the 2nd to 4th submodule (=MSI submodule), the value status 0 indicates that the value
is incorrect or the basic submodule has not yet been configured (not ready).
The following figure shows the assignment of the address space with submodules 1 and 2
and the value status.
Figure 4-3
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Address space for configuration as 1 x 16-channel DI 16x24VDC HF MSI
DI 16x24VDC HF Digital Input Module (6ES7521-1BH00-0AB0)
Manual, 08/2018, A5E03485952-AG